What determines the number and size of the seeds produced by a plant? How often should it reproduce them? How often should a plant produce them? Why and how are seeds dispersed, and what are the implications for the diversity and composition of vegetation? These are just some of the questions tackled in this wide-ranging review of the role of seeds in the ecology of plants. The authors bring together information on the ecological aspects of seed biology, starting with a consideration of reproductive strategies in seed plants and progressing through the life cycle, covering seed maturation, dispersal, storage in the soil, dormancy, germination, seedling establishment, and regeneration in the field. The text encompasses a wide range of concepts of general relevance to plant ecology, reflecting the central role that the study of seed ecology has played in elucidating many fundamental aspects of plant community function.

The ecology of seeds

Succession is a process of continuous colonization of and extinction on a site by species populations. The process has long been central in ecological thinking; much theory and many data about succession have accumulated over the years. Since nearly all species in all communities participate in successional interactions, and because physiological ecology encompasses everything that a plant does during its life cycle, a complete review of physiological ecology of all species in all successions is not possible. Thus in this review I discuss the physiological adaptations of species of one successional gradient-from open field to broad-leaved deciduous forest. I concentrate on the physiological adaptations of early successional plants to environmental variability and collate the literature on tree physiology to make comparisons with early successional plants. My discussion may not be applicable to seres where there is little difference in physiognomy between early and late successional plants or where the designation of species as early or late successional is unjustified (e.g. for certain desert and tundra habitats). I discuss the nature of successional environments, seed germination, seedling and mature plant development, plant growth, photosynthesis, water use, and the physiological ecology of competition and interference.

https://www.jstor.org/stable/info/2096796

The Physiological Ecology of Plant Succession

Contents

Summary  11

1Introduction  12
2Why does NO make a good signal?  12
3NO biosynthesis  13
4NO biology  17
5NO signal transduction  23
6Conclusion  30

Acknowledgements  31


References  31



Summary
Recently nitric oxide (NO) has emerged as a key signalling molecule in plants. Here we review the potential sources of endogenous NO, outline the biological processes likely to be mediated by NO, and discuss the downstream signalling processes by which NO exerts its cellular effects. It will be important to develop methods to quantify intracellular NO synthesis and release. Clasification of the biosynthetic origins of NO is also required. NO can be synthesised from nitrite via nitrate reductase (NR) and although biochemical and immunological data indicate the presence of enzyme(s) similar to mammalian nitric oxide synthase (NOS), no NOS genes have been identified. NO can induce various processes in plants, including the expression of defence-related genes and programmed cell death (PCD), stomatal closure, seed germination and root development. Intracellular signalling responses to NO involve generation of cGMP, cADPR and elevation of cytosolic calcium, but in many cases, the precise biochemical and cellular nature of these responses has not been detailed. Research priorities here must be the reliable quantification of downstream signalling molecules in NO-responsive cells, and cloning and manipulation of the enzymes responsible for synthesis and degradation of these molecules.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1046/j.1469-8137.2003.00804.x

Nitric oxide signalling in plants

Germination—Still a mystery

*Summary At harvest, sunflower (Helianthus annuus L.) seeds are dormant and unable to germinate at temperatures below 15 � C. Seed storage in the dry state, known as after-ripening, is associated with an alleviation of embryonic dormancy allowing subsequent germination at suboptimal temperatures. To identify the process by which dormancy is broken during after-ripening, we focused on the role of reactive oxygen species (ROS) in this phenomenon. After-ripening entailed a progressive accumulation of ROS, namely superoxide anions and hydrogen peroxide, in cells of embryonic axes. This accumulation, which was investigated at the cellular level by electron microscopy, occurred concomitantly with lipid peroxidation and oxidation (carbonylation) of specific embryo proteins. Incubation of dormant seeds for 3 h in the presence of hydrogen cyanide (a compound that breaks dormancy) or methylviologen (a ROS-generating compound) also released dormancy and caused the oxidation of a specific set of embryo proteins. From these observations, we propose a novel mechanism for seed dormancy alleviation. This mechanism involves ROS production and targeted changes in protein carbonylation patterns.

/pdf/ros-production-and-protein-oxidation-as-a-novel-mechanism-1k6132o34e.pdf

ROS production and protein oxidation as a novel mechanism for seed dormancy alleviation.

Action and uptake of azides, nitrates, nitrites, hydroxylamines, and ammonium salts were measured on germination of Amaranthus albus, Lactuca sativa, Phleum pratense, Barbarea vulgaris, B verna , and Setaria glauca seeds Nitrate and nitrite reductase activities were measured in vivo for each of these kinds of seeds Activities were measured in vitro for catalase, peroxidase, glycolate oxidase, and pyridine nucleotide quinone reductase on extracts of A albus and L sativa seeds before and after germination The enzymic activities measured and the responsiveness of the haemproteins to inhibition by the several compounds indicate that nitrites, azides, and hydroxylamines promote seed germination by inhibition of H 2 O 2 decomposition by catalase Ammonium salts showed pronounced promotive activity only for B verna and B vulgaris seeds, for which they served as metabolic substrates The promotion of germination is thought to depend on coupling of peroxidase action to NADPH oxidation, which can regulate the pentose pathway of d-glucose 6-phosphate use Pyridine nucleotide quinone reductase is the possible coupling enzyme This enzyme and others required for the action are present in the seeds before imbibition of water

Promotion of seed germination by nitrate, nitrite, hydroxylamine, and ammonium salts.

Light fromii sunlight, incandescent, an(l fluorescent sources was filtered through fresh tobacco (Nicotiana tabaccuml L.), corn (Zea mays L.), anid soybean (Glycine max (L.) Merrill) leaves. The spectral quality of the leaf-filtered light showed that much more of the incident red energy was absorbed than the far-red. The effect of the leaf-filtered light on the phytochrome-controlled germination of six weed species was generally to inhibit germination of seeds given a stimulatory pre-irradiation of red light from a standard source. Germination of seeds with no pre-irradiation was either not promoted or promoted to various degrees. Unfiltered light, at intensities equivalent to those uinder the leaf filters, caused no comparable effects. These results indicate an effect of altered spectral quality of the leaf-filtered light on the ratio of inactive/active phytochrome (Pr/Pfr) in the underlying seeds. We suggest that such phenomena could influence the germination of weed seeds in the fiell.

Light Filtration by Foliar Canopies: Significance for Light-Controlled Weed Seed Germination'

Dormancy in fall panicum (Panicum dichotomiflorum Michx.) caryopses (seeds) is overcome by imbibition at 35° C in ethanol solutions. Whereas germination in the absence of ethanol depends on active phytochrome, the seeds may germinate in darkness after treatment with 0.2 to 0.5 M ethanol. Ethanol overcomes dormancy also in seeds of several other weedy grass species. Ethyl ether, chloroform, methanol, and acetone act similarly to ethanol. We suggest that this action depends on modifyng the properties of a membrane(s) in a manner related to the actions of other anesthetics.

Overcoming dormancy in seeds with ethanol and other anesthetics.

Potassium cyanide at 3 mum to 10 mm promotes germination of Amaranthus albus, Lactuca sativa, and Lepidium virginicum seeds. l-Cysteine hydrogen sulfide lyase, which catalyzes the reaction of HCN with l-cysteine to form beta-l cyanoalanine, is active in the seeds. beta-l-Cyanoalanine is the most effective of the 23 alpha-amino acids tested for promoting germination of A. albus seeds. Aspartate, which is produced by enzymatic hydrolysis of asparagine formed by hydrolysis from beta-cyanoalanine, is the second most effective of the 23 amino acids. Uptake of aspartate-4-(14)C is much lower than of cyanide.Radioactive tracer in K(14)CN shows uptake of about 1.5 mumoles of HCN per gram of A. albus and L. sativa seeds after 20 hours of imbibition. Extracts of the seeds gave high (14)C activity in beta-cyanoalanine, asparagine, and aspartate. The acid-hydrolyzed protein extract gave high activity only in aspartate. Tests were negative for free cyanide in the seed. Respiration of the seed is inhibited more than 75% by KCN and by KN(3) at 10 mm. Azide at greater than 1.0 mm inhibits the promotion of germination by cyanides. Neither 0.1 mm KCN nor KN(3) inhibit O(2) consumption, whereas lower concentrations promote germination. It is concluded that the high rate of utilization of cyanide in the reaction to form beta-l-cyanoalanine and the subsequent incorporation into protein limit any inhibition of oxygen consumption. The promotion of seed germination is substrate-limited by asparagine-aspartate, which is required for protein synthesis.

Promotion of seed germination by cyanide.

MANY viable seeds fail to germinate in darkness after imbibing water, but do so to varying degrees in solutions of several compounds. Well known promoters of germination are nitrate, nitrite and various sulphydryl and gibberellin salts1. Hydroxylammonium salts, although often cited as inhibitory1, are known to promote germination at low concentrations2. The essential action of none of these is understood and the use of nitrates in seed testing remains empirical. In seeking underlying causes for the promotive effects of nitrates we examined the germination responses to other nitrogenous salts as well as compounds affecting respiration. Cyanides were found to promote germination of many kinds of seeds in extension of the observations of Roberts3.

R. B. Taylorson

Papers

Promotion of seed germination by nitrate, nitrite, hydroxylamine, and ammonium salts.

Light Filtration by Foliar Canopies: Significance for Light-Controlled Weed Seed Germination'

Overcoming dormancy in seeds with ethanol and other anesthetics.

Promotion of seed germination by cyanide.

Promotion of Seed Germination by Nitrates and Cyanides