Aspects Of Plant Reproduction Research Articles

Habitat fragmentation and population features differently affect fruit predation, fecundity and offspring performance in a non-specialist gypsum plant.

The effects of habitat fragmentation on plant populations are complex, as it might disrupt many ecological processes, including plant reproduction and plant-animal interactions. Gypsum specialist plants may be resilient to fragmentation due to their evolutionary history in fragmented landscapes, but the effects on non-specialist plants occurring in gypsum are unknown. We conducted a study focusing on different aspects of the reproductive cycle of Astragalus incanus subsp. incanus, a plant facultatively linked to gypsum soils. We focused on plant fecundity and pre-dispersal predation, obtained from field observations, and offspring performance, assessed in a common garden. Beyond fragment size and connectivity, we also considered habitat quality, population size and density and plant size as predictors. Fragment size and connectivity had no effect on plant fecundity, but jointly determined fruit predation, while fragment size was positively related to offspring growth. Population density, rather than population size, had a positive effect on predation but negatively affected plant fecundity and offspring performance. Habitat quality reduced both plant fecundity and predation incidence. In this non-specialist species, habitat fragmentation, population features and habitat quality affect different facets of plant performance. Predation was the only process clearly affected by fragmentation variables, fecundity mainly depended on population features and offspring performance and was better explained by mother plant identity. Our results show the need to consider habitat and population features together with fragment size and connectivity in order to assess the effects of fragmentation. Importantly, these effects can involve different aspects of plant reproduction, including plant-animal interactions.

Reactive Oxygen Species as Mediators of Gametophyte Development and Double Fertilization in Flowering Plants.

Reactive oxygen species (ROS) are toxic by-products of aerobic metabolism. In plants, they also function as important signaling molecules that regulate biotic and abiotic stress responses as well as plant growth and development. Recent studies have implicated ROS in various aspects of plant reproduction. In male gametophytes, ROS are associated with germline development as well as the developmentally associated programmed cell death of tapetal cells necessary for microspore development. ROS have a role in regulation of female gametophyte patterning and maintenance of embryo sac polarity. During pollination, ROS play roles in the generation of self-incompatibility response during pollen-pistil interaction, pollen tube growth, pollen tube burst for sperm release and fertilization. In this mini review, we provide an overview of ROS production and signaling in the context of plant reproductive development, from female and male gametophyte development to fertilization.

MADS-Box and bHLH Transcription Factors Coordinate Transmitting Tract Development in Arabidopsis thaliana.

The MADS-domain transcription factor SEEDSTICK (STK) controls several aspects of plant reproduction. STK is co-expressed with CESTA (CES), a basic Helix-Loop-Helix (bHLH) transcription factor-encoding gene. CES was reported to control redundantly with the brassinosteroid positive signaling factors BRASSINOSTEROID ENHANCED EXPRESSION1 (BEE1) and BEE3 the development of the transmitting tract. Combining the stk ces-4 mutants led to a reduction in ovule fertilization due to a defect in carpel fusion which, caused the formation of holes at the center of the septum where the transmitting tract differentiates. Combining the stk mutant with the bee1 bee3 ces-4 triple mutant showed an increased number of unfertilized ovules and septum defects. The transcriptome profile of this quadruple mutant revealed a small subset of differentially expressed genes which are mainly involved in cell death, extracellular matrix and cell wall development. Our data evidence a regulatory gene network controlling transmitting tract development regulated directly or indirectly by a STK-CES containing complex and reveal new insights in the regulation of transmitting tract development by bHLH and MADS-domain transcription factors.

Patterns and sources of variation in pollen deposition and pollen tube formation in flowers of the endemic monoecious shrub Cnidoscolus souzae (Euphorbiaceae).

Pollen deposition and pollen tube formation are key components of angiosperm reproduction but intraspecific variation in these has rarely been quantified. Documenting and partitioning (populations, plants and flowers) natural variation in these two aspects of plant reproduction can help uncover spatial mosaics of reproductive success and underlying causes. In this study, we assess variation in pollen deposition and pollen tube formation for the endemic monoecious shrub Cnidoscolus souzae throughout its distribution range in Mexico, and determine how this variation is structured among populations, plants and flowers. We also infer the relative importance of pollen quantity and quality in determining pollination success in this species. While we found no evidence suggesting that pollen receipt limits C.souzae reproduction across 19 populations, we did find extensive variation in pollen load size and pollen tube number per flower. Total variation in pollen receipt and pollen tube number was mostly explained by intra-individual and among-population variance. Furthermore, pollen load size had a stronger effect on the number of pollen tubes at the base of the style than pollen germination rate, suggesting that pollen quantity may be more important than quality for pollen tube success in C.souzae. Our results suggest that both small within-plant flower differences and broad-scale differences in community attributes can play an important role in determining pollination success. We emphasise the need to evaluate patterns and sources of variation in pollen deposition and pollen tube formation as a first step in understanding the causes of variation in pollination success over broad spatial scales.

Structural basis for the oligomerization of the MADS domain transcription factor SEPALLATA3 in Arabidopsis.

In plants, MADS domain transcription factors act as central regulators of diverse developmental pathways. In Arabidopsis thaliana, one of the most central members of this family is SEPALLATA3 (SEP3), which is involved in many aspects of plant reproduction, including floral meristem and floral organ development. SEP3 has been shown to form homo and heterooligomeric complexes with other MADS domain transcription factors through its intervening (I) and keratin-like (K) domains. SEP3 function depends on its ability to form specific protein-protein complexes; however, the atomic level determinants of oligomerization are poorly understood. Here, we report the 2.5-Å crystal structure of a small portion of the intervening and the complete keratin-like domain of SEP3. The domains form two amphipathic alpha helices separated by a rigid kink, which prevents intramolecular association and presents separate dimerization and tetramerization interfaces comprising predominantly hydrophobic patches. Mutations to the tetramerization interface demonstrate the importance of highly conserved hydrophobic residues for tetramer stability. Atomic force microscopy was used to show SEP3-DNA interactions and the role of oligomerization in DNA binding and conformation. Based on these data, the oligomerization patterns of the larger family of MADS domain transcription factors can be predicted and manipulated based on the primary sequence.

Tropical forest fragmentation limits pollination of a keystone understory herb.

Loss of native vegetation cover is thought to be a major driver of declines in pollination success worldwide. However, it is not well known whether reducing the fragmentation of remaining vegetation can ameliorate these negative effects. We tested the independent effects of composition vs. configuration on the reproductive success of a keystone tropical forest herb (Heliconia tortuosa). To do this we designed a large-scale mensurative experiment that independently varied connected forest-patch size (configuration) and surrounding amount of forest (composition). In each patch, we tested whether pollen tubes, fruit, and seed set were associated with these landscape variables. We also captured hummingbirds as an indication of pollinator availability in a subset of patches according to the same design. We found evidence for an effect of configuration on seed set of H. tortuosa, but not on other aspects of plant reproduction; proportion of seeds produced increased 40% across the gradient in patch size we observed (0.64 to > 1300 ha), independent of the amount of forest in the surrounding landscape at both local and landscape scales. We also found that the availability of pollinators was dependent upon forest configuration; hummingbird capture rates increased three and one-half times across the patch size gradient, independent of forest amount. Finally, pollinator availability was strongly positively correlated with seed set. We hypothesize that the effects of configuration on plant fitness that we observed are due to reduced pollen quality resulting from altered hummingbird availability and/or movement behavior. Our results suggest that prioritizing larger patches of tropical forest may be particularly important for conservation of this species.

Cysteine-Rich Peptides (CRPs) mediate diverse aspects of cell-cell communication in plant reproduction and development

Cell-cell communication in plants is essential for the correct co-ordination of reproduction, growth, and development. Studies to dissect this mode of communication have previously focussed primarily on the action of plant hormones as mediators of intercellular signalling. In animals, peptide signalling is a well-documented intercellular communication system, however, relatively little is known about this system in plants. In recent years, numerous reports have emerged about small, secreted peptides controlling different aspects of plant reproduction. Interestingly, most of these peptides are cysteine-rich, and there is convincing evidence suggesting multiple roles for related cysteine-rich peptides (CRPs) as signalling factors in developmental patterning as well as during plant pathogen responses and symbiosis. In this review, we discuss how CRPs are emerging as key signalling factors in regulating multiple aspects of vegetative growth and reproductive development in plants.

Reproduction and Horticultural Performance of Transgenic Ethylene-insensitive Petunias

A series of experiments on ethylene-insensitive (EI) petunia plants (Petunia ×hybrida Hort. Vilm.-Andr.) generated in two genetic backgrounds were conducted to determine the involvement of ethylene in horticultural performance. Experiments examined various aspects of horticultural performance: days to flower, flower senescence after pollination and without pollination, fruit set and ripening, and adventitious root formation on vegetative stem cuttings. The development of EI plants was altered in several ways. Time from seed sowing to first flower anthesis was decreased by a week for EI plants grown at 26/21 °C. Flower senescence in nonpollinated and self-pollinated flowers was delayed in all EI plants compared to wild-type plants. Fruit set percentage on EI plants was slightly lower than on wild-type plants and fruit ripening on EI plants was delayed by up to 7 days. EI plants produced fewer commercially acceptable rooted cuttings than wild-type plants. There was a basic difference in the horticultural performance of the two EI lines examined due to a difference in the genetic backgrounds used to generate the lines. EI plants displayed better horticultural performance when grown with day/night temperatures of 26/21 °C than 30/24 °C. These results suggest that tissue-specific ethylene insensitivity as well as careful consideration of the genetic background used in transformation procedures and growth conditions of etr1-1 plants will be required to produce commercially viable transgenic floriculture crops. EI petunias provide an ideal model system for studying the role of ethylene in regulating various aspects of plant reproduction.

Call for application to the course: Molecular and cellular aspects of plant reproduction 28 April – 4 May 1996, Nijmegen

Call for application to the course: Molecular and cellular aspects of plant reproduction 28 April – 4 May 1996, Nijmegen

A Negative Correlation Between Growth and Rainfall in a Tropical Liana

The vegetative phenology of Passiflora pittieri, a liana, was monitored for nine months in Corcovado National Park, Costa Rica. Corcovado is tropical premontane wet forest with a dry season from January to April. A time-series analysis of shoot production and rainfall revealed a significant seasonal trend in shoot production, high during the dry season and low during the wet season, and a strong negative correlation between shoot production and current rainfall even after removal of the seasonal trend from the data. Apparently, P. pittieri was able to respond immediately to some factor associated with dry spells. Evidence is also presented for an endogenous inhibition of shoot initiation following shoot production. Possible factors that regulate shoot production are also discussed. MOST PHENOLOGICAL STUDIES IN THE TROPICS have been primarily concerned with flowering and fruiting (Fournier and Salas 1966, Nevling 1971, Opler et al. 1976, Stiles 1978, Augspurger 1983). However, vegetative phenology may underlie many aspects of plant reproduction. Borchert (1983) stated . . the timing of flower induction and its possible controls are virtually unknown for all tropical trees and can only be inferred from an analysis of seasonal shoot growth patterns in conjunction with tree morphology. In fact, vegetative phenology can determine seasonal changes in net primary productivity (Lieth 1970) and can influence many attributes of forest structure and regeneration. Frankie et al. (1974) classified trees in a tropical wet forest as having either continuous leafing, discontinuous production of new leaves, or marked leaf drop and flushing. Many studies of tropical vegetative phenology are of trees that have marked leaf drop and flushing; studies of dry forest trees predominate (Janzen 1967, Daubenmire 1972, Reich and Borchert 1984). Frankie et al. (1974) and Opler et al. (1980) found that 28 percent of the overstory tree species, 40 percent of the understory tree species, and about half' of the shrub and treelet species in a tropical wet forest exhibited continuous leaf production. Yet very few studies investigate in more detail the temporal variation of growth in such plants. Trees have been the focus of almost all phenological studies. Trees are large populations of meristems connected in very complicated ways. Putz (1979) emphasized the difficulty of identifying phenological events in many Malaysian trees because of variable shoot behavior within trees. The phenology of lianas, important components of many tropical forests (Putz 1983, 1984), has been ignored, even though they are excellent candidates for such studies. Their greatly reduced number of meristems and simpler architecture is conducive to detailed investigations of vegetative growth. As part of a study on plant-herbivore interactions, I investigated the temporal variation of shoot production and its relationship to rainfall in a woody liana, Passiflora pittieri, in a wet forest in Costa Rica. Time-series analysis, a method that could be applied more frequently in phenological studies (see Putz 1979), was used to characterize rainfall and shoot production by the population of lianas. Analysis of shoot production by individual plants also allowed investigation of endogenous control of growth. The genus Passiflora contains largely herbaceous neotropical vines, but one subgenus, Astrophea, contains many species that are woody lianas and small trees (Killip 1938). Passiflora pittieri is a species of Astrophea widespread in Costa Rica and Panama (Longino 1984). In contrast to most other Passiflora, P. pittieri is a shade-tolerant species found most often in the understory of wet forest. It is a woody liana with a single, strong taproot. Mature leaves are dark green, glabrous, coriaceous, elliptic to oblanceolate, and vary in size from 2 to 30 cm long. Unsupported plants in the undergrowth have a shrubby aspect. On all but the largest plants, sympodial shoots are produced one at a time, often with a month or more between successive shoots. Large plants may produce more than one shoot simultaneously. Shoots rapidly elongate for 2 to 3 wk before growth ceases and leaves harden. Very small plants produce short shoots with one to three small leaves. Shrubby plants, the majority in this study, produce shoots that are 50 to 150 cm long with 10 to 20 leaves. Additional information on the biology of P. pittieri is presented in Longino (1984).