Salicylhydroxamic Acid Mimics Esterase-like Action

Salicylhydroxamic acid (SHAM), an inhibitor of the alternativerespiratory pathway, reacts with 2', 7'-dichlorofluorescin diacetate(DCFH-DA) and fluorescein diacetate to form 2', 7'-dichlorofluorescinand fluorescein, respectively. These reactions show that SHAMpossesses esterase-like activity. As SHAM may act on endogenousacetoxymethyl ester-type compounds, assessment of respirationpatterns of cells requires cautious interpretation, especiallyduring prolonged incubation. Key words: Salicylhydroxamic acid, respiration, alternative pathway, viability test     

After-effect of Water Stress on Stomatal Opening Potential: I. TECHNIQUES AND MAGNITUDES

The after-effect of a period of water stress upon the light-openingability of stomata was studied in tobacco (Nicotiana tabaccum)and broad bean (Vicia faba). Stomatal opening was always measuredafter floating leaf discs on water under favourable conditionsof light and temperature to obtain maximal opening at full leafturgor. Thus possible interference due to persistence of leaf-waterdeficits in the post-stress leaves was eliminated. Stomatalaperture was accurately estimated using a resistance porometer;values so obtained were substantiated by the direct measurementof aperture. Two to 4 days of wilting of tobacco, producing leaf-water deficitsof 30 to 40 per cent, had a marked after-effect on tobacco stomata.The ability to open in light was depressed and complete recoveryfrom this depression required 2 to 5 days after rewatering.In some cases over-recovery was observed; this was probablyrelated to a physiologically younger condition of leaves ofstressed plants following turgor recovery. In beans similarstresses caused after-effects smaller in magnitude but qualitativelysimilar to those in tobacco. In both tobacco and beans the magnitudeof the after-effect was approximately proportional to the leaf-waterdeficit attained immediately prior to rewatering.     

Effects of Temperature and Various Red or Far-red Irradiations on Phytochrome- and Gibberellin A3-mediated Germination Control in Partially Hydrated Lettuce Seeds

Dark reversion of phytochrome in partially hydrated lettuceseeds (Lactuca sativa cv. Grand Rapids) is temperature dependent.After initial red irradiation (R) the higher the storage temperature,the higher the dark reversion rate. Following dark moist storage(DMS) at 30 ?C for 15 d none of the seeds receiving initialR germinated, whereas seeds stored at 0 ?C germinated nearlyas well (about 80%) as unstored controls. The half-time fordark reversion at 20 ?C and 30 ?C is 9 d and 3 d respectively.Repeated R treatments given at 5 d intervals during DMS at 20?C and 30 ?C maintained a high germination capacity. With threeor more R treatments the effect of high temperature largelydisappeared. Dark reversion of phytochrome was not observed in partiallyhydrated lettuce seeds receiving continuous red irradiation(cont R) for two or more days. The promotive effect of contR could be reversed at any time with a brief far-red irradiation(FR), indicating that the phytochrome system remained fullyphototransformable. With continuous far-red light (cont FR)the ability of gibberellin A₃ (GA₃) to stimulate germinationdisappeared and response to GA₃ also diminished in cont R followedby FR but at a slower rate indicating the induction of secondarydormancy in these partially hydrated seeds. This induction ofdormancy was retarded by repetitive or cont R but was enhancedby cont FR. The results of this study suggest a role for theaccumulated stable intermediates of phytochrome transformationin partially hydrated seeds with repeated or continuous R treatmentsand different effects of GA₃ and R in the regulation of germination. Key words: Phytochrome, Lactuca sativa, Seed germination, Temperature, Dark reversion of phytochrome, Seed water content     

Genetic diversity and microgeographic differentiation of Yushan cane (Yushania niitakayamensis; Poaceae) in Taiwan

Yushan cane ( Yushania niitakayamensis ) is distributed in southeast Asia. In Taiwan, the species occurs in mountains 1000–3600 m above sea level. The species appears to spread mainly by rhizomes and flowers only rarely. Nine locations across its distribution range in Taiwan were sampled. Locations at higher altitudes generally consist of grassland and forest undergrowth habitats while those of lower altitudes generally consist of forest undergrowth only. Thus two sampling sites (montane grassland and forest undergrowth) were selected from each location at higher altitudes while only one sampling site was selected from each location at lower altitudes, resulting in a total of 13 sampling sites. Within each sampling site, 20 individual plants were sampled. The results of the cluster analysis and the principal coordinate analysis based on random amplified polymorphic DNA (RAPD) indicated that the populations are generally differentiated according to geographical separation and altitudinal differences that interrupt gene flow. The populations at higher altitudes, where the species is distributed somewhat contiguously, were found to be more similar genetically. Analysis of molecular variance ( AMOVA ) revealed that the among-location, between sampling sites within location, and among individuals within sampling site components accounted for 15.27%, 4.80% and 79.93% of the total variance, respectively. For locations with two sampling sites, two-level AMOVA revealed that the diversities between sampling sites (sun and shade habitats) within locations ranged from 2.91% to 7.99% of the total diversity. Random permutation tests revealed that these diversities were significant, implying that there is microgeographic differentiation due to habitat differences.