The glycine betaine which accumulated in shoots of young barley plants (Hordeum vulgare L.) during an episode of water stress did not undergo net destruction upon relief of stress, but its distribution among plant organs changed. During stress, betaine accumulated primarily in mature leaves, whereas it was found mainly in young leaves after rewatering. Well-watered, stressed, and stressed-rewatered plants were supplied with [methyl-(14)C]betaine (8.5 nmol) via an abraded spot on the second leaf blade, and incubated for 3 d. In all three treatments the added (14)C migrated more or less extensively from the second leaf blade, but was recovered quantitatively from various plant organs in the form of betaine; no labeled degradation products were found in any organ. When 0.5 μmol of [methyl-(14)C]betaine was applied via an abraded spot to the second leaf blades of well-watered, mildly-stressed, and stressed-rewatered plants, (14)C was translocated out of the blades at velocities of about 0.2-0.3 cm/min which were similar to velocities found for applied [(14)C]sucrose. Heat-girdling of the sheath prevented export of [(14)C]betaine from the blade. When 0.5 μmol [(3)H]sucrose and 0.5 μmol [(14)C]betaine were suppled simultaneously to second leaf blades, the (3)H/(14)C ratio in the sheath tissue was the same as that of the supplied mixture. After supplying tracer [(14)C]betaine aldehyde (the immediate precursor of betaine) to the second leaf blade, the (14)C which was translocated into the sheath was in the form of betaine. Thus, betaine synthesized by mature leaves during stress behaves as an inert end product and upon rewatering is translocated to the expanding leaves, most probably via the phloem. Accordingly, it is suggested that the level of betaine in a barley plant might serve as a useful cumulative index of the water stress experienced during growth.

A barley (Hordeum vulgare L.) mutant ("cool") with leaf transpiration unaffected by the application of 1 mM abscisic acid (ABA) was isolated from the population of M2 seedlings using thermography (electronic visualization, and quantitation of the temperature profiles on the surface of the leaves). Stomata of the mutant plants were insensitive to exogenously applied ABA, darkness, and such desiccation treatments as leaf excision and drought stress. The evaporative cooling of the leaves of the "cool" barley was always higher than that of the wild-type barley, even without ABA application, indicating that the diffusive resistance of the mutant leaves to water loss was always lower. Guard-cell morphology and stomatal density as well as ABA level and metabolism were seemingly unaltered in the mutant plants. In addition, gibberellin-induced α-amylase secretion and precocious embryo germination in the mutant barley was inhibited by ABA to the same extent as in the wild-type barley.

Somatic embryos were induced on cotyledonary explants of cucumber (Cucumis sativus, L. cv. Clinton). The somatic embryo tissue was induced and multiplied on a semisolid medium. The greatest vitrification and expansion of explants were observed when 0.15% Gelrite was the gelling agent. At the induction stage, explants on a medium gelled with 0.7% agar yielded more somatic embryo tissue, uncontaminated by callus, than explants on either Gelrite (0.15%, 0.3%, and 0.6%) or on 1.4% or 0.35% agar. In contrast to the induction stage, there was no effect of gelling agent on the fresh weight of putative somatic embryo tissue produced during the multiplication stage. When sucrose, glucose, or fructose was the sugar source in the multiplication medium, similar weights of tissue were produced. However, when sucrose was compared with fructose in the presence of either agar or Gelrite as gelling agent, the subsequent germination of the somatic embryos was higher when the tissue was multiplied on Gelrite in the presence of 3% sucrose. Maltose (3%) severely inhibited tissue multiplication.

Summary. Several unrelated compounds are known to selectively inhibit the development of the male gametophyte. When applied at suitable dosages to plants at the appropriate stages of anther development, these substances block the formation of fertile pollen. The affected stage of pollen development is characteristic of the specific chemical structure of the compound, ranging from effects on microspore meiosis to the formation of pollen defective in the ability to germinate or fertilize. The range of effects mediated by these substances, and by known male-sterile mutants, indicates that microspore development has several critical phases that are particularly sensitive to fatal inhibition. We propose that chemical inhibitors of pollen development deserve attention as tools for elucidating the regulation of pollen development.

The accumulation of betaine (glyclnebetalne, N,N,N‐trimethylglycine) in barley (Hordeum vulgate L.) during water stress may be of adaptive value. The objective of this research was to evaluate the variability for betalne level among genotypes of H. vulgare and H. spontaneum C. Koch in preparation for a physiological‐genetic assessment of the adaptive value of betaine accumulation. Betaine was determined using either a pyrolysis/gas chromatographic method or a periodide spectrophotometric assay, specially modified for screening. In controlled environment tests, 339 genotypes were grown to the four‐leaf stage under well‐watered conditions and analyzed for shoot betaine level; 145 of these were also tested under water‐stressed conditions. There were significant differences for betaine level among genotypes, both without and with water stress (approximate ranges of betaine levels: 10 to 40 μmol/g dry wt in well‐watered conditions; 35 to 90 μtmol/g dry wt under stress). The betaine levels of stressed plants were significantly correlated with those of unstressed plants of the same genotype. Thirteen H. vulgare cultivars which were high and low accumulators in controlled environments were grown in the field under simulated dryland conditions and betaine was analyzed in the upper leaves. At the ear emergence stage, significant variation for betaine level was observed among cultivars although there were no significant differences in their water status. Those cultivars that accumulated either high or low levels of betaine in controlled environments accumulated respectively high or low levels in the field, the correlation among cultivars in the two environments was highly significant (r = 0.71). These results indicate that genotypic variability for betaine level is expressed in both controlled environments and in the field, and that this variability is unlikely to be due solely to variability for water status. Physiological‐genetic studies of the adaptive role of betaine may thus be possible.