Plant Polyamines in Reproductive Activity and Response to Abiotic Stress*

Abstract

Abstmct:In this review we will focus on two areas in which the accumulated evidence for a critical physiological role of polyamines is becoming compelling, i.e. reproductive activity and response to abiotic stress. Regarding reproductive behavior, it seems clear that polyamines are members of the array of internal compounds required for flower initiation, normal floral organ morphogenesis. fruit growth and fruit ripening in particular plant species. Abiotic stresses such as osmotic stress can "turn on" arginine decarboxylase (ADC) genes, resulting in a rapid increase in their mRNA levels. Localization of ADC enzyme in the chloroplast suggests a role of PAS in the maintenance of photosynthetic activity during senescence responses induced by osmotic stress. We envisage that the use of transgenic plants and improved molecular probes will resolve in the near future the physiological significance of stress-induced changes in PA metabolism as well as the role of these compounds in reproductive activity.

Polyamine levels in the seagrass Cymodocea nodosa

“…This is a relative decrease of free spm in C. nodosa leaves, shown in the increase of the put/spm and spd/spm ratios. The diamine spm has been identified as an anti-senescence-inducing factor (Galston et al, 1997), thus, this accumulation of put relative to spm could be the factor promoting the senescence of the leaf. At the time of the year when the samples were collected (August), the meadow generally starts to lose leaves after reaching its biggest area.…”

Polyamines: potent modulators of plant responses to stress

“…The use of inhibitors permitted the elucidation of a compensatory reaction accompanying the switching off some PA biosynthesis, which is of importance for understanding the mechanism of plant-cell homeostasis, especially under stress conditions (Galston et al 1997). A number of investigators have used inhibitors of PA to modulate the cellular PAs level in order to determine their role in various plant processes.…”

Deoxyhypusine Synthase from Tobacco

“…With respect to the ubiquitous occurrence of putrescine (51), it is still unresolved whether homospermidine is synthesized in vivo in tobacco without being accumulated in detectable amounts or whether the formation of homospermidine is the result of indiscriminate enzyme activity detectable only in vitro. The occurrence of homospermidine has not been reported for tobacco, although this plant is rather frequently used in polyamine research (52)(53)(54). However, a recent GC-MS analysis of the polyamine fraction of young tobacco leaves revealed very small but unambiguously detectable amounts of homospermidine.…”

“…This function is still unknown. Among plant physiologists, the suspected but unknown roles of spermidine in plant growth and development are controversially discussed (52)(53)(54)(55). The requirement of spermidine as an essential substrate for deoxyhypusine formation provides direct evidence for a function of this polyamine in plant metabolism.…”