Morphological and Biochemical Characteristics of a Novel Albino Tea Cultivar (Camellia sinensis ‘Geumda’)

Abstract

Tea plant [Camellia sinensis (L.) O. Kuntze] is an economically important evergreen crop cultivated worldwide. While most tea plants have green leaves, albino cultivars with yellow or white young leaves have attracted growing interest due to their elevated levels of L-theanine, a key compound that enhances the umami flavor and overall quality of green tea. In this study, we characterized the morphological and biochemical traits of a novel albino tea cultivar, ‘Geumda’, developed in Korea. ‘Geumda’ exhibited yellow young shoots during the first flush and smaller leaves compared to the green-leaf standard cultivar, ‘Sangmok’. Although the catechin content of ‘Geumda’ was lower than that of ‘Sangmok’, it exhibited significantly higher levels of total amino acids, L-theanine, and arginine by 2.1-, 2.0-, and 9.8-fold, respectively. Transmission electron microscopy and gene expression analysis revealed that the elevated amino acid content in ‘Geumda’ was associated with impaired chloroplast development, leading to reduced chlorophyll content and diminished photosynthetic capacity. These findings suggest that ‘Geumda’, with its high concentrations of theanine and arginine and its impaired chloroplast development, represents a valuable genetic resource for the production of functional green teas enriched in umami flavor and beneficial health properties.

1. Introduction

The tea plant [Camellia sinensis (L.) O. Kuntze] is an economically important evergreen crop cultivated worldwide. Tea is primarily produced from the leaves of three varieties: C. sinensis var. sinensis, C. sinensis var. assamica, and C. sinensis var. pubilimba [1]. Various tea germplasms have been identified with elevated levels of anthocyanins, catechins, amino acids, aromatic compounds, or chlorophylls, as well as reduced caffeine content [2,3,4]. Tea leaves contain a wide range of primary and secondary metabolites, notably amino acids, catechins, and their derivatives, which play essential roles in determining tea quality [5]. Among these, theanine and catechins are regarded as key quality indicators and are also known for their physiological benefits, such as vascular prevention and anti-obesity effects [6,7,8,9,10].

While most cultivated tea plants have green leaves, non-green-leaf cultivars have been developed, and tea products made from these cultivars are gaining popularity due to their distinctive flavor profiles and visual appeal [11,12]. In particular, albino tea leaves, typically yellow or white, have been reported to contain higher levels of theanine compared to their green-leaf counterparts [13]. Theanine contributes not only to the umami taste and good quality of green tea but also possesses functional properties, including stress reduction, neuroprotection, and potential modulation of mood and cognition [14,15,16,17]. Thus, albino tea plants are considered valuable genetic resources for green tea production, owing to both their distinctive appearance and the enhanced taste and health benefits conferred by high theanine content [18,19].

Albino tea plant leaves are classified into three types based on their coloration: albino, etiolated, and variegated, and they are further categorized into temperature-sensitive and light-sensitive mutant groups [18]. Temperature-sensitive mutants produce white or yellow young shoots at temperatures below 20 °C, which revert to green as the temperature rises [20]. ‘Baiye 1’, originated from China, is a representative temperature-sensitive cultivar [21]. In contrast, light-sensitive mutants exhibit yellowish albino leaves in response to high light intensity; ‘Huangjinya’ and ‘Baijiguan’ are typical examples of this type [18,22].

Abnormal chloroplast development is a hallmark of albino tea leaves under specific environmental conditions [23,24]. In green leaves, the chloroplasts of mesophyll cells contain well-organized thylakoids structures, whereas albino leaves exhibit disorganized or underdeveloped thylakoids [25]. These structural defects impair the biosynthesis of photosynthetic pigments, such as chlorophylls and carotenoids [23,26], leading to reduced photosynthetic activity. The decline in photosynthesis disrupts the balance between carbon and nitrogen (N) metabolism, thereby stimulating N assimilation pathways and promoting the accumulation of amino acids, particularly theanine [25,27,28].

Despite increasing global interest in albino tea cultivars for their unique appearance and high levels of functional metabolites, no such cultivar had been officially developed or registered in Korea until recently. In response to the growing demand for high-quality, health-promoting tea products, we sought to develop and characterize a novel albino tea cultivar adapted to the Korean agro-climatic environment. The primary objectives of this study were to investigate its morphological traits, chloroplast development, and metabolic composition, with a particular focus on amino acids and catechin profiles.

Through long-term field evaluation, we identified a promising yellow-leaf albino line from wild tea germplasms collected in Gurye-gun, Jeollanam-do, Korea. This line exhibited stable expression of the albino phenotype under open-field conditions and was officially registered as a new Korean tea cultivar under the name ‘Geumda’ on 20 March 2025. Here, we provide a comprehensive characterization of ‘Geumda’, including its growth characteristics, chlorophyll content, chloroplast ultrastructure, photosynthesis-related gene expression, and profiles of key biochemical constituents.

2. Materials and Methods

2.1. Plant Materials and Cultivation

‘Geumda’ and ‘Sangmok’ tea plants were planted at an experimental tea field of the Research Institute of Climate Change and Agriculture, NIHHS, located on Jeju Island, Republic of Korea (33.468487, 126.518109) in 2020. ‘Geumda’ is a yellow-leaf albino tea line originally collected from a wild plant population in Gurye-gun, Jeollanam-do, Korea. This cultivar has been submitted for plant variety protection to Korea Seed & Variety Service (KSVS, http://seed.go.kr/sites/seed_eng/index.do, accessed on 8 May 2024) (Application No. 2024-50). ‘Sangmok’ is a green-leaf cultivar developed by the Rural Development Administration (RDA), Korea. The cultivar was derived from seeds of landrace tea plants collected in 1998 from a native green tea habitat in Wolchul Mountain, Yeongam-gun, Jeollanam-do. After regional adaptability trials, it was submitted for plant variety protection in 2011 and registered with KSVS in 2014 (Application No. 2011-426).

2.2. Investigation of Growth Characteristics and Leaf Size of Tea Plants

The growth characteristics of ‘Geumda’ and ‘Sangmok’ were investigated according to the UPOV examination standards (2020.09.02 ver.), translated by KSVS. A total of 33 items, consisting of 22 items of quantitative characteristics, 5 items of pseudo-qualitative characteristics, and 6 items of qualitative characteristics, were visually observed and scored.

For the leaf size comparison, mature leaves were used. On 8 September 2022, the length, width, and thickness of the third leaf from a bud were measured using a digital caliper. Five individuals per cultivar were evaluated, with two different leaves measured per individual. Leaf area was calculated using the following formula: Leaf area (cm²) = Leaf length (cm) × Leaf width (cm) × 0.7.

2.3. Measurement of Chlorophyll Content

Chlorophyll content was measured from April to August 2022 on the second leaf from a bud using a portable chlorophyll meter (SPAD-502, Konica Minolta, Osaka, Japan). The measurements were conducted on five individuals per cultivar, with five different leaves measured per individual.

2.4. Chloroplast Ultrastructure Observation by Transmission Electron Microscopy (TEM)

TEM observation was performed according to the method described as follows. Young shoots collected at the first harvest time were initially fixed in Karnovsky’s fixative at 4 °C overnight. Samples were post-fixed in 1% (v/v) osmic acid or 2 h at room temperature, followed by staining with 0.5% (v/v) uranyl acetate at 4 °C overnight. The fixed samples were dehydrated through a graded ethanol series (50, 50, 75, 90, 100, and 100% v/v) for 10 min per step. After dehydration, samples were treated with propylene oxide and embedded in Spurr’s resin. Ultra-thin sections (80 nm) were prepared using an EM UC7 ultratome (Leica, Wetzlar, Germany) and observed at 100 kv under Carl Zeiss Leo912AB transmission electron microscopy (Carl Zeiss, Oberkochen, Germany).

2.5. Determination of Free Amino Acids Content

At first harvest time in 2023, young shoots (a bud and three leaves) of ‘Geumda’ and ‘Sangmok’ were collected, freeze-dried, and finely ground. The powdered tea sample (0.5 g) was extracted with hot water (10 mL) for 10 min, with vortexing every 5 min. The extracts were centrifuged at 6000 rpm for 10 min, and the supernatants were well mixed with an equal amount of 5% trichloroacetic acid (0.5 mL) solution. The mixtures were centrifuged again at 10,000 rpm for 10 min. The final supernatant was diluted 10-fold with 0.02 N HCL and filtered through a 0.2 μm nylon syringe filter. The filtrate (20 μL) was analyzed using an automatic amino acid analyzer (LA8080, Hitachi High-Tech Science Corp., Tokyo, Japan). The conditions were as follows: the column: Hitachi custom ion exchange resin, 4.6 mm ID × 60 mm; the mobile phase: protein hydrolysate analysis buffers (PH Kanto, PH-1, PH-2, PH-3, PH-4, and PJ-RG, Kanto Chemical Co., Inc., Tokyo, Japan); the coloring kit for analysis: a Ninhydrin Coloring Solution kit (Fujifilm Wako Pure Chemical Corp., Osaka, Japan); flow rate: 0.35 mL/min; detection wavelengths: 570 nm for most amino acids and 440 nm for theanine. The contents of amino acids and theanine were expressed as mg per g of dry weight (mg/g DW). All samples were analyzed in triplicate.

2.6. Determination of Catechin Content

The freeze-dried, ground tea sample (0.02 g) was mixed with 100% methanol (1 mL) using a vortex mixer, followed by sonication at 60 °C for 25 min (JAC-4020, Jeio Tech, Daejeon, Korea). The extract was centrifuged at 13,000 rpm for 10 min and filtered through a 0.2 μm nylon syringe filter. The filtrate was diluted 10-fold with 100% methanol. The diluted sample (20 μL) was injected into a UPLC system (Waters, Milford, MA, USA) equipped with an ACQITY UPLC HSS T3 column (1.8 μm, 2.1 × 100 mm, Waters, Milford, MA, USA) maintained at 30 °C. The mobile phases were 0.1% (v/v) acetic acid in distilled water (A) and 0.1% (v/v) acetic acid in acetonitrile (B), with a flow rate of 0.2 mL/min. The gradient elution program was as follows: 95% A for 3 min, decreased to 75% A for 12 min and 40% A for 13 min, maintained at 40% A until 16 min, increased back to 95% A by 17 min, and maintained until 22 min. Catechins were detected at 280 nm. All samples were analyzed in triplicate. Standard compounds, (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC), catechin, and (-)-epicatechin (EC), were purchased from Sigma-Aldrich (St. Louis, MO, USA) compounds. The total catechin content was calculated as the sum of EGCG, ECG, EGC, and EC.

2.7. RNA Extraction and Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) Analysis

For gene expression analysis, young shoots of the tea cultivars were collected at harvest time in 2025, immediately frozen in liquid nitrogen, and ground into a fine powder using a pestle and mortar. Total RNA was extracted using the RNeasy^® Plant Mini Kit (Cat. No. 74904, Qiagen, Hilden, Germany) according to the manufacturer’s instructions. First-strand cDNA was synthesized from 1 µg of total RNA using the QuantiTect^® Reverse Transcription kit (Cat. No. 205311, Qiagen, Hilden, Germany). The qRT-PCR was performed using the CFX96 Touch™ Real-Time PCR Detection System (Bio-Rad, Hercules, CA, USA) with iTaq Universal SYBR^® Green Supermix (Bio-Rad, Hercules, CA, USA). The PCR conditions were as follows: initial denaturation at 95 °C for 5 min, followed by 40 cycles of 95 °C for 20 s, 60 °C for 20 s, and 72 °C for 20 s. The melting curve analysis was conducted by measuring fluorescence at 0.2 °C increments from 55 °C to 95 °C. Each cDNA sample was analyzed in triplicate. The expression of target genes was normalized to the internal reference gene 18S rRNA [26], and relative expression levels were calculated using the 2^−ΔΔCt formula [29]. All samples were analyzed in triplicate. All qRT-PCR primer sequences used in this study are listed in Table S1.

2.8. Statistical Analysis

Data are presented as mean ± standard deviation (SD) from three independent biological replicates. Statistical significance between the ‘Geumda’ and ‘Sangmok’ groups was determined using Student’s t-test. Differences were considered statistically significant at p < 0.05.

3. Results

3.1. Growth Characteristics of ‘Geumda’

‘Geumda’ showed a distinct phenotype compared to conventional green-leaf tea cultivars when grown under open-field conditions. As shown in Figure 1, the young shoots of ‘Geumda’ displayed a yellow coloration in April 2022, while those of ‘Sangmok’ were light green. To figure out the phenotypic characteristics of ‘Geumda’, a total of 33 items were visually observed (

Table 1. Phenotypic characteristics of the albino cultivar ‘Geumda’ and the green-leaf standard cultivar ‘Sangmok’.

	Characteristics	Phenotypes	Score	Geumda	Sangmok
1 1 (*) 2 QN	Plant: vigor	Weak Middle Strong	3 5 7	3	5
2 (*) 3 PQ	Plant: type	Shrub Semi-arbor Arbor	1 2 3	1	1
3 (*) QN	Plant: growth habit	Upright Semi-upright Spreading	1 3 5	3	3
4 QN	Plant: density of branches	Sparse Medium Dense	3 5 7	3	3
5 4 QL	Branch: zigzagging	Absent Present	1 9	1	1
6 (*) 5 (+) QN	Young shoot: time of beginning of ‘one and a bud’ stage	Early Medium Late	3 5 7	5	3
7 PQ	Young shoot: color of second leaf at ‘two and a bud’ stage	Whitish Yellow Yellow-green Light green Middle green Purple-green	1 2 3 4 5 6	2	4
8 (*) QL	Young shoot: pubescence of a bud	Absent Present	1 9	9	9
9 QN	Young shoot: density of pubescence of a bud	Sparse Medium Dense	3 5 7	3	3
10 QL	Young shoot: anthocyanin coloration at base of the petioles	Absent Present	1 9	1	1
11 (*) QN	Young shoot: length of ‘three and a bud’	Short Medium Long	3 5 7	3	5
12 (*) QN	Leaf blade: attitude	Upwards Outwards Downwards	1 3 5	3	3
13 (*) QN	Leaf blade: length	Short Medium Long	3 5 7	5	5
14 (*) QN	Leaf blade: width	Narrow Medium Broad	3 5 7	5	5
15 QN	Leaf blade: shape	Very narrow elliptic Narrow elliptic Medium elliptic Wide elliptic	1 2 3 4	3	3
16 QN	Leaf blade: intensity of green color	Light Medium Dark	3 5 7	3	7
17 QN	Leaf blade: shape in cross section	Folded upwards Flat Recurved	1 2 3	2	2
18 QN	Leaf blade: texture of upper surface	Smooth or weakly rugose Moderately rugose Strongly rugose	3 5 7	5	3
19 PQ	Leaf blade: shape of apex	Obtuse Acute Acuminate	1 2 3	2	2
20 QN	Leaf blade: undulation of margin	Absent or weak Medium Strong	3 5 7	3	3
21 QN	Leaf blade: serrations on the margin	Weak Medium Strong	3 5 7	3	5
22 PQ	Leaf blade: shape of base	Acute Obtuse Truncate	1 2 3	2	1
23 QN	Flower: time of full flowering	Early Medium Late	3 5 7	7	3
24 QN	Flower: length of pedicel	Short Medium Long	3 5 7	3	5
25 (*) QL	Flower: pubescence on outer side of sepal	Absent Present	1 9	9	9
26 (*) QL	Flower: anthocyanin coloration on outer side of sepal	Absent Present	1 9	1	1
27 (*) QN	Flower: diameter	Small Medium Large	3 5 7	3	5
28 (+) PQ	Flower: color of inner petals	Greenish White Pink	1 2 3	2	2
29 (*) QL	Flower: pubescence of ovary	Absent Present	1 9	9	9
30 QN	Flower: density of pubescence of ovary	Sparse Medium Dense	3 5 7	7	7
31 QN	Flower: length of style	Short Medium Long	3 5 7	3	5
32 (+) QN	Flower: position of style splitting	Low Medium High	3 5 7	7	5
33 (*) (+) QN	Flower: position of stigma relative to stamens	Below Same level Above	3 5 7	3	5

¹ (*): Important characteristics for the international harmonization of variety descriptions; ² QN: Quantitative characteristic; ³ PQ: Pseudo-qualitative characteristic; ⁴ QL: Qualitative characteristic; ⁵ (⁺): Additional important phenotypic characteristics distinguishing ‘Geumda’ from standard cultivar.

).

‘Geumda’ exhibited weaker vigor than that of ‘Sangmok’ and displayed a semi-upright growth habit with sparse branching and no observable branch bending. The emergence of one leaf and a bud occurred later in ‘Geumda’ (7 April 2022) than in ‘Sangmok’ (27–31 March 2022). The length of three leaves and a bud was shorter in ‘Geumda’ than in ‘Sangmok’.

Similar to ‘Sangmok’, ‘Geumda’ showed sparse pubescence of a bud and no anthocyanin coloration at the base of the petioles. Both cultivars shared several leaf traits, including an outward leaf blade attitude, medium leaf size, elliptic shape, flat cross-sectional shape, acute leaf apex, and absent or weak margin undulation. However, ‘Geumda’ had a lighter green color, a more rugose upper surface, weaker marginal serration, and a more obtuse leaf base shape.

Flower morphology was also largely similar between the two cultivars, with both exhibiting pubescence on the sepal, white inner petals, and dense pubescence on the ovary. Nevertheless, ‘Geumda’ flowered later and exhibited a smaller flower diameter, shorter pedicel and style, a higher position of style splitting, and a stigma positioned below the stamens relative to ‘Sangmok’.

In terms of leaf size, ‘Geumda’ had significantly smaller mature leaves than ‘Sangmok’ (

Table 2. Size of the third leaf from a bud of the albino cultivar ‘Geumda’ and the green-leaf standard cultivar ‘Sangmok’ in the fourth harvest time (September 2022).

	Geumda	Sangmok
Length (cm)	6.64 ± 0.72 ***	8.22 ± 0.48
Width (cm)	2.96 ± 0.46 *	3.41 ± 0.31
Thickness (mm)	0.41 ± 0.06	0.47 ± 0.06
Leaf area (cm2)	13.85 ± 3.04 ***	19.68 ± 2.62

The results are presented as means ± SD (n = 10). Significant differences between ‘Geumda’ and ‘Sangmok’ were determined using Student’s t-test, expressed with asterisks (* p < 0.05; *** p < 0.001).

). The average length, width, and thickness of ‘Geumda’ leaves were 6.64 ± 0.72 cm, 2.96 ± 0.46 cm, and 0.41 ± 0.06 mm, respectively, compared to 8.22 ± 0.48 cm, 3.41 ± 0.31 cm, and 0.47 ± 0.06 mm in ‘Sangmok’. The smaller leaf area of ‘Geumda’ was primarily due to its reduced leaf length and width.

3.2. Chlorophyll Content of ‘Geumda’

Given that leaf color is influenced by chlorophyll content [30] and ‘Geumda’ exhibits yellow young shoots, chlorophyll content was monitored from April to August 2022. ‘Geumda’ showed consistently lower chlorophyll levels compared to ‘Sangmok’ throughout the period (Figure 2). In April, the chlorophyll content of ‘Geumda’ was 5.0 ± 1.5 μmol/m², which was only 13% of the level observed in ‘Sangmok’ (39.9 ± 7.3 μmol/m²). Although chlorophyll content increased in both cultivars over time, ‘Geumda’ maintained significantly lower levels (10~58% of ‘Sangmok’).

3.3. Abnormal Chloroplast Development of ‘Geumda’

Leaf albinism is often associated with defective chloroplast development. To investigate this, the ultrastructure of the chloroplasts in ‘Geumda’ was examined using TEM. As shown in Figure 3, the chloroplasts in the yellow leaves of ‘Geumda’ were poorly developed or scarcely present, whereas the chloroplasts in ‘Sangmok’ were clearly observed. High-magnification TEM images revealed that the density of grana and thylakoids in ‘Geumda’ chloroplasts was significantly reduced.

To further understand the molecular basis of chloroplast development, we analyzed the expression levels of genes involved in chloroplast biogenesis and photosynthesis. Genes encoding photosynthesis I and II subunits (Psa B, Pas E, Psa G and Psb B), the components of the cytochrome b6f complex (Pet A, Pet F), light-harvesting chlorophyll-binding proteins (Lhca3, Lhcb4), and the enzymes involved in chlorophyll biosynthesis (hemL, E3.1.1.14, PCR) were all significantly downregulated in the young shoots of ‘Geumda’ compared to those of ‘Sangmok’ (Figure 4).

3.4. Contents of Quality-Related Compounds: Amino Acids and Catechins

Albino tea cultivars are well known for their elevated levels of amino acids, particularly theanine [18]. In agreement with this, ‘Geumda’ contained significantly higher total free amino acid levels than ‘Sangmok’. At the first harvest, the total free amino acid content was 62.48 ± 3.38 mg/g DW in ‘Geumda’ compared to 30.00 ± 6.52 mg/g DW in ‘Sangmok’ (

Table 3. Profiles of free amino acids in the young shoots of the albino cultivar ‘Geumda’ and the green-leaf standard cultivar ‘Sangmok’ at the time of first harvest.

	Geumda	Sangmok
Total free amino acids	62.48 ± 3.38 **	30.00 ± 6.52
Theanine	54.47 ± 3.29 **	27.31 ± 6.00
Aspartic acid	1.24 ± 0.03 ***	0.45 ± 0.01
Glutamic acid	1.78 ± 0.18 **	0.95 ± 0.19
Serine	0.64 ± 0.05 **	0.28 ± 0.02
Threonine	0.14 ± 0.02 *	0.07 ± 0.00
Alanine	0.24 ± 0.02 **	0.09 ± 0.02
Valine	0.07 ± 0.00 **	0.04 ± 0.00
Leucine	0.07 ± 0.00 ***	0.02 ± 0.00
Lysine	0.16 ± 0.02	ND
Histidine	0.13 ± 0.01	ND
Arginine	2.86 ± 0.11 ***	0.29 ± 0.00
Cysteine	0.02 ± 0.00	0.02 ± 0.00
Methionine	0.02 ± 0.00	ND
Isoleucine	0.02 ± 0.01	ND
Phenylalanine	0.04 ± 0.01	ND
Taurine	0.02 ± 0.00	0.02 ± 0.00
Citrulline	0.05 ± 0.03	0.05 ± 0.01
Ornithine	0.42 ± 0.03	0.39 ± 0.06
Gamma-aminobutyric acid	0.06 ± 0.01	0.04 ± 0.01

The results are presented as means ± SD mg/g DW (n = 3). ND: Non-detected significant differences between ‘Geumda’ and ‘Sangmok’ were determined using Student’s t-test, expressed with asterisks (* p < 0.05; ** p < 0.01; *** p < 0.001).

). Theanine was the most abundant amino acid, comprising 54.47 ± 3.29 mg/g DW in ‘Geumda’ and 27.31 ± 6.00 mg/g DW in ‘Sangmok’. In addition to theanine, other free amino acids, such as aspartic acid, glutamic acid, serine, glutamine, alanine, arginine, and gamma-aminobutyric acid, were also more abundant in ‘Geumda’ than in ‘Sangmok’ (Table 3), indicating a pronounced enhancement of nitrogen metabolism.

In contrast, catechin content showed an inverse trend. The total catechin content in the young shoots of ‘Geumda’ was 76.86 ± 3.13 mg/g DW, including EGCG (37.44 ± 1.05 mg/g DW), EGC (15.26 ± 1.25 mg/g DW), EC (6.78 ± 0.33 mg/g DW), and ECG (16.85 ± 0.56 mg/g DW). Meanwhile, ‘Sangmok’ exhibited significantly higher levels of total catechins (125.34 ± 2.29 mg/g DW), with EGCG (51.07 ± 0.82 mg/g DW), EGC (43.29 ± 1.27 mg/g DW), EC (13.59 ± 0.21 mg/g DW), and ECG (16.37 ± 0.16 mg/g DW) (Figure 5).

4. Discussion

To date, 26 tea cultivars have been officially registered in Korea; among them, ‘Geumda’ is the first albino tea cultivar with yellow leaves, while the remaining 25 cultivars have green leaves [31]. Among green-leaf tea cultivars, Sangmok (C. sinensis L. ‘Sangmok’), used as the control in this study, is a Korean standard tea cultivar. Its genomic information has recently become available, with the complete chloroplast genome sequenced in 2020 [32] and the nuclear genome assembled at the chromosome level in 2024 [33]. Genomic analysis revealed that ‘Sangmok’ possesses several cultivar-specific genes involved in catechin biosynthesis, including members of the ANR, DFR, F3H, LAR, and cytochrome P450 gene families, which may play roles in anti-inflammatory, antiviral, antibacterial, and insect defense mechanisms [33].

This study presents the morphological and biochemical characteristics of the newly developed albino tea cultivar, ‘Geumda’. Under field conditions, ‘Geumda’ exhibited a distinct phenotype, including yellow young shoots and small leaves, compared to ‘Sangmok’ (Figure 1 and Table 1 and Table 2). The chlorophyll content of ‘Geumda’ was significantly lower than that of ‘Sangmok’ (Figure 2), which was further confirmed by TEM analysis showing underdeveloped chloroplasts with a severely reduced density of grana and thylakoids (Figure 3). These structural defects are consistent with previous findings in other albino tea cultivars, such as ‘Baiye 1’ and ‘Huangjinya’, in which disruptions in chloroplast development have been associated with pale leaf coloration and diminished photosynthetic activity [18,26,27,34,35].

Gene expression analysis further confirmed the physiological basis of this phenotype. Key genes related to photosynthesis and chlorophyll biosynthesis, including PsaB, PetA, Lhca3, Lhcb4, hemL, PCR, and others, were significantly downregulated in the young shoots of ‘Geumda’ (Figure 4). This widespread suppression of photosynthesis-related genes has also been reported in other albino tea cultivars, ‘Zhonghuang1’ (ZH1) and ‘ZH 2’, where transcriptomic, proteomic, and microarray data analyses identified the downregulation of genes involved in photosynthesis Ⅰ/Ⅱ and chlorophyll synthesis as central mechanisms underlying the albinism [26,35]. Our results suggest that in ‘Geumda’, the suppression of genes involved in chloroplast development and chlorophyll biosynthesis under specific environmental conditions leads to defective chloroplast formation, reduced chlorophyll accumulation, and, ultimately, the albino phenotype. Among albino tea types, temperature-sensitive cultivars are known to display severe chloroplast damage and reduced pigment levels at low-temperature conditions [20,36,37]. In ‘Geumda’, yellow buds began to emerge in early April, and the ‘one bud and three leaves’ stage was typically observed around 20 April, when the daily mean temperature remained below 20 °C (Figure S1). As temperatures rose above this in June, the yellow leaves turned green (Figure S2). This temperature-dependent color change suggests that ‘Geumda’ may belong to the temperature-sensitive albino type. However, further research is needed to elucidate the environmental and genetic factors regulating these traits.

Previous studies have proposed that impaired chloroplast development in albino leaves reduces carbon assimilation, which subsequently activates nitrogen metabolic pathways as a compensatory response [18,38]. This metabolic shift is reflected in ‘Geumda’, with a significantly higher accumulation of total free amino acids, particularly theanine (Table 3). In ‘Geumda’, total free amino acids and theanine, the key contributor to the umami flavor of green tea, accounted for approximately 6.3% and 5.5% of dry leaf weight, respectively, which is within the typical range reported for an albino cultivar (6–7% total amino acids; 2–5% theanine) and substantially higher than those in green-leaf cultivars (3–4% total amino acids; 1–2% theanine) [12,39].

In contrast, the catechin levels in ‘Geumda’ were significantly reduced compared to that in ‘Sangmok’ (Figure 5). This inverse relationship between amino acids and catechins is a hallmark of albino tea phenotypes and reflects the suppression of phenylpropanoid pathways activity under photosynthetic deficiency [27,40]. When taken together, these results indicate that ‘Geumda’ exhibits enhanced nitrogen metabolism and suppressed carbon assimilation, which underlie its high amino acid (especially theanine) and low catechin profile. These metabolic features not only contribute to the umami-rich flavor of ‘Geumda’ but also suggest potential health benefits, given the reported roles of theanine in stress reduction and alleviation of depressive symptoms [41].

Considering these functional attributes, ‘Geumda’ represents a high-value cultivar for the development of premium and health-promoting tea products. Nonetheless, further studies using omics approaches, such as transcriptomics and metabolomics, are required to clarify the regulatory networks underlying its unique phenotype and flavor chemistry.

More broadly, the development of ‘Geumda’ marks a significant milestone in Korean tea breeding. As a cultivar derived from native wild germplasm, ‘Geumda’ demonstrates stable expression of the albino trait under open-field conditions and enriches the genetic diversity of domestic tea cultivars. Its release opens new possibilities for producing premium-quality green teas tailored to consumer preferences for flavor and function.

5. Conclusions

In this study, we comprehensively characterized the morphological, physiological, and biochemical traits of ‘Geumda’, a newly developed albino tea cultivar derived from native Korean germplasm. ‘Geumda’ exhibited significantly reduced chlorophyll content due to impaired chloroplast development and the downregulation of photosynthesis-related genes. This photosynthetic deficiency caused an imbalance between carbon and nitrogen metabolism, leading to a substantial accumulation of amino acids—particularly theanine and arginine—while catechin levels were substantially lower than those in the green-leaf cultivar ‘Sangmok’. This high amino acid and low-catechin profile is characteristic of albino tea cultivars and contributes to the enhanced umami flavor and potential health benefits of the tea. When taken together, ‘Geumda’ represents a valuable genetic resource for the production of premium and functional green tea products while also contributing to the diversification of Korean tea germplasm. These findings provide a solid foundation for further omics-based research aimed at elucidating the regulatory mechanisms of albinism and amino acid accumulation in tea plants.