Special Issue "Pollen Tube Growth 2016"

A special issue of Plants (ISSN 2223-7747).

Deadline for manuscript submissions: closed (31 October 2016).

Special Issue Editor

Prof. Dr. Giampiero Cai
E-Mail Website
Guest Editor
Department of Life Sciences, University of Siena, Siena, Italy
Interests: plant cell cytoskeleton; cell wall; organelle movement; cell morphogenesis; plant reproduction
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Pollen and pollen tubes are vectors by which male gametes are delivered to egg cells for fertilization in higher plants. As such, they have a fundamental role in plant reproduction by allowing gene transfer and propagation of seed plants. In angiosperms, pollen tubes grow within the style of receptive flowers and exchange signals and information that regulate (either negatively or positively) the growth rate of pollen tubes. Signaling between pollen tubes and pistils is critical to promote and guide pollen tube growth, but also to avoid inbreeding and outcrossing through recognition and rejection of self- or incompatible pollen. Therefore, pollen tubes are a model system for the study of cell–cell interaction and cell guidance in plants. Key genes and molecules involved in pollen tube guidance have been partially identified but a general model by which they orchestrate tube growth is still missing.

Growth of pollen tubes occurs essentially at the tip, where a number of secretory vesicles accumulate thereby providing material for cell wall and plasma membrane. In this region, external signals are perceived, interpreted and used to regulate the growth rate. In recent years, identification of RAC/ROP GTPases, their recruitment to cell membrane and activation in response to external signals are becoming progressively clear allowing to decipher the mechanism of signal perception and transduction, as well as the regulation of cellular processes (such as growing within pistils and delivering of sperms to the female gametophyte). Important components of the signal transduction mechanism are ion flux, intracellular ion gradients and dynamics, which are critical for the polarization of pollen tubes and for maintaining the growth site at the tip. Understanding how these features are related to the signal transduction pathway is an important challenge.

Signaling is interfaced to the dynamics of exocytosis and endocytosis, whose precise balance regulates pollen tube growth at the apex and whose perturbation causes significant changes to tube morphology. Exo- and endocytosis regulates assembly and deposition of the cell wall, which is critical for pollen tube growth and, more generally, for global morphogenesis of plants. A number of evidences describe the composition of the pollen tube cell wall, but little is known about the molecular mechanism controlling cell wall deposition. Nevertheless, we are progressively appreciating how callose and cellulose are synthetized, deposited, and designed to be load-bearing and resistant to tensile forces. Secretion, modification and dynamics of pectins are also progressively elucidating but an outlook of how the synthesis of cell wall polymers is interplayed is still missing as well as their relationship with the signal transduction pathway. Deposition of cell wall and accumulation of secretory vesicles are both dependent on the dynamics of the cytoskeleton, whose activity is regulated by both motor and non-motor proteins. The precise balance between polymerized and unpolymerized cytoskeletal filaments (coupled to the dynamic interplay between cytoskeleton and motor proteins) supports the continuous supply of secretory vesicles to the tip. Regulation of cytoskeleton activity is likely to be dependent on both signal transduction pathway and ion dynamics.
In view of this amazing interplay between different molecular processes (from ion dynamics to membrane transport), pollen tubes are now considered an excellent model by which investigating the mechanism of cell shaping and the interaction between mechanical problems and their biological control. This Special Issue on “Pollen Tube Growth” (which is a continuation/update of the previous call ended in 2012) is focused on researches aimed at improving our current knowledge of the molecular mechanisms controlling pollen tube growth, from perception of extracellular signals to cytoskeleton-based delivery of cell wall components to integration of such mechanisms into global processes that determine the shape and growth of pollen tubes and, ultimately, fertilization in plants.

Prof. Dr. Giampiero Cai
Guest Editor

Manuscript Submission Information

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Keywords

  • pollen tube growth
  • fertilization in higher plants
  • signal transduction
  • intracellular ion gradients
  • exocytosis and endocytosis
  • cell wall synthesis
  • cytoskeleton dynamics
  • system tip growth model

Published Papers (4 papers)

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Research

Open AccessArticle
Pollen Grain Preservation and Fertility in Valuable Commercial Rose Cultivars
Plants 2017, 6(2), 17; https://doi.org/10.3390/plants6020017 - 24 Apr 2017
Cited by 2
Abstract
In the cut flower market, traditional breeding is still the best way to achieve new rose cultivars. The geographical delocalization of cultivar constitution (generally made in Europe and North America) and plant cultivation (large areas in Africa and South America) represents a limit [...] Read more.
In the cut flower market, traditional breeding is still the best way to achieve new rose cultivars. The geographical delocalization of cultivar constitution (generally made in Europe and North America) and plant cultivation (large areas in Africa and South America) represents a limit point for crossing and selection. Rose breeders often need to overcome geographical distances, resulting in asynchrony in flowering among crossing parents, by storing and sending pollen. Hence, a key aspect in breeding programs is linked to pollen availability and conservation, jointly with the identification of parameters related to pollen fertility. In this study we present the results of three different trials. In the first, pollen diameter and pollen viability were chosen as fertility predictors of 10 Rosa hybrida commercial cultivars. In the second trial, aliquots of dried pollen grains of six R. hybrida cultivar were stored under two different temperatures (freezer at T = −20 °C and deep freezer at T = −80 °C) and after a wide range of conservation period, their viability was measured. In the third trial, the effective fertilization capacity of frozen pollen of 19 pollen donor cultivars was evaluated during 2015 crossing breeding plan, performing 44 hybridizations and correlating the number of seeds and the ratio seeds/crossing, obtained by each cultivar, with in vitro pollen germination ability. Full article
(This article belongs to the Special Issue Pollen Tube Growth 2016)
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Open AccessArticle
Perturbation Analysis of Calcium, Alkalinity and Secretion during Growth of Lily Pollen Tubes
Plants 2017, 6(1), 3; https://doi.org/10.3390/plants6010003 - 30 Dec 2016
Cited by 7
Abstract
Pollen tubes grow by spatially and temporally regulated expansion of new material secreted into the cell wall at the tip of the tube. A complex web of interactions among cellular components, ions and small molecule provides dynamic control of localized expansion and secretion. [...] Read more.
Pollen tubes grow by spatially and temporally regulated expansion of new material secreted into the cell wall at the tip of the tube. A complex web of interactions among cellular components, ions and small molecule provides dynamic control of localized expansion and secretion. Cross-correlation studies on oscillating lily (Lilium formosanum Wallace) pollen tubes showed that an increase in intracellular calcium follows an increase in growth, whereas the increase in the alkaline band and in secretion both anticipate the increase in growth rate. Calcium, as a follower, is unlikely to be a stimulator of growth, whereas the alkaline band, as a leader, may be an activator. To gain further insight herein we reversibly inhibited growth with potassium cyanide (KCN) and followed the re-establishment of calcium, pH and secretion patterns as growth resumed. While KCN markedly slows growth and causes the associated gradients of calcium and pH to sharply decline, its removal allows growth and vital processes to fully recover. The calcium gradient reappears before growth restarts; however, it is preceded by both the alkaline band and secretion, in which the alkaline band is slightly advanced over secretion. Thus the pH gradient, rather than the tip-focused calcium gradient, may regulate pollen tube growth. Full article
(This article belongs to the Special Issue Pollen Tube Growth 2016)
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Open AccessFeature PaperArticle
Cold Tolerance of the Male Gametophyte during Germination and Tube Growth Depends on the Flowering Time
Plants 2017, 6(1), 2; https://doi.org/10.3390/plants6010002 - 29 Dec 2016
Cited by 1
Abstract
In temperate climates, most plants flower during the warmer season of the year to avoid negative effects of low temperatures on reproduction. Nevertheless, few species bloom in midwinter and early spring despite severe and frequent frosts at that time. This raises the question [...] Read more.
In temperate climates, most plants flower during the warmer season of the year to avoid negative effects of low temperatures on reproduction. Nevertheless, few species bloom in midwinter and early spring despite severe and frequent frosts at that time. This raises the question of adaption of sensible progamic processes such as pollen germination and pollen tube growth to low temperatures. The performance of the male gametophyte of 12 herbaceous lowland species flowering in different seasons was examined in vitro at different test temperatures using an easy to handle testing system. Additionally, the capacity to recover after the exposure to cold was checked. We found a clear relationship between cold tolerance of the activated male gametophyte and the flowering time. In most summer-flowering species, pollen germination stopped between 1 and 5 °C, whereas pollen of winter and early spring flowering species germinated even at temperatures below zero. Furthermore, germinating pollen was exceptionally frost tolerant in cold adapted plants, but suffered irreversible damage already from mild sub-zero temperatures in summer-flowering species. In conclusion, male gametophytes show a high adaptation potential to cold which might exceed that of female tissues. For an overall assessment of temperature limits for sexual reproduction it is therefore important to consider female functions as well. Full article
(This article belongs to the Special Issue Pollen Tube Growth 2016)
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Open AccessArticle
Plant Responses to Climate Change: The Case Study of Betulaceae and Poaceae Pollen Seasons (Northern Italy, Vignola, Emilia-Romagna)
Plants 2016, 5(4), 42; https://doi.org/10.3390/plants5040042 - 06 Dec 2016
Cited by 4
Abstract
Aerobiological data have especially demonstrated that there is correlation between climate warming and the pollination season of plants. This paper focuses on airborne pollen monitoring of Betulaceae and Poaceae, two of the main plant groups with anemophilous pollen and allergenic proprieties in Northern [...] Read more.
Aerobiological data have especially demonstrated that there is correlation between climate warming and the pollination season of plants. This paper focuses on airborne pollen monitoring of Betulaceae and Poaceae, two of the main plant groups with anemophilous pollen and allergenic proprieties in Northern Italy. The aim is to investigate plant responses to temperature variations by considering long-term pollen series. The 15-year aerobiological analysis is reported from the monitoring station of Vignola (located near Modena, in the Emilia-Romagna region) that had operated in the years 1990–2004 with a Hirst spore trap. The Yearly Pollen Index calculated for these two botanical families has shown contrasting trends in pollen production and release. These trends were well identifiable but fairly variable, depending on both meteorological variables and anthropogenic causes. Based on recent reference literature, we considered that some oscillations in pollen concentration could have been a main effect of temperature variability reflecting global warming. The duration of pollen seasons of Betulaceae and Poaceae, depending on the different species included in each family, has not unequivocally been determined. Phenological responses were particularly evident in Alnus and especially in Corylus as a general moving up of the end of pollination. The study shows that these trees can be affected by global warming more than other, more tolerant, plants. The research can be a contribution to the understanding of phenological plant responses to climate change and suggests that alder and hazelnut trees have to be taken into high consideration as sensible markers of plant responses to climate change. Full article
(This article belongs to the Special Issue Pollen Tube Growth 2016)
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