Abscisic Levels Research Articles

Barley Genotypes Vary in Stomatal Responsiveness to Light and CO2 Conditions.

Changes in stomatal conductance and density allow plants to acclimate to changing environmental conditions. In the present paper, the influence of atmospheric CO2 concentration and light intensity on stomata were investigated for two barley genotypes—Barke and Bojos, differing in their sensitivity to oxidative stress and phenolic acid profiles. A novel approach for stomatal density analysis was used—a pair of convolution neural networks were developed to automatically identify and count stomata on epidermal micrographs. Stomatal density in barley was influenced by genotype, as well as by light and CO2 conditions. Low CO2 conditions resulted in increased stomatal density, although differences between ambient and elevated CO2 were not significant. High light intensity increased stomatal density compared to low light intensity in both barley varieties and all CO2 treatments. Changes in stomatal conductance were also measured alongside the accumulation of pentoses, hexoses, disaccharides, and abscisic acid detected by liquid chromatography coupled with mass spectrometry. High light increased the accumulation of all sugars and reduced abscisic acid levels. Abscisic acid was influenced by all factors—light, CO2, and genotype—in combination. Differences were discovered between the two barley varieties: oxidative stress sensitive Barke demonstrated higher stomatal density, but lower conductance and better water use efficiency (WUE) than oxidative stress resistant Bojos at saturating light intensity. Barke also showed greater variability between treatments in measurements of stomatal density, sugar accumulation, and abscisic levels, implying that it may be more responsive to environmental drivers influencing water relations in the plant.

MaMADS2 repression in banana fruits modifies hormone synthesis and signalling pathways prior to climacteric stage

BackgroundWhile the role of ethylene in fruit ripening has been widely studied, the contributions of additional plant hormones are less clear. Here we examined the interactions between the transcription factor MaMADS2-box which plays a major role in banana fruit ripening and hormonal regulation. Specifically, we used MaMADS2 repressed lines in transcriptome and hormonal analyses throughout ripening and assessed hormone and gene expression perturbations as compared to wild-type (WT) control fruit.ResultsOur analyses revealed major differences in hormones levels and in expression of hormone synthesis and signaling genes mediated by MaMADS2 especially in preclimacteric pulp. Genes encoding ethylene biosynthesis enzymes had lower expression in the pulp of the repressed lines, consistent with reduced ethylene production. Generally, the expression of other hormone (auxin, gibberellins, abscisic acid, jasmonic acid and salicylic acid) response pathway genes were down regulated in the WT pulp prior to ripening, but remained high in MaMADS2 repressed lines. Hormone levels of abscisic acid were also higher, however, active gibberellin levels were lower and auxin levels were similar with MaMADS2 repression as compared to WT. Although abscisic level was higher in MaMADS2 repression, exogenous abscisic acid shortened the time to ethylene production and increased MaMADS2 mRNA accumulation in WT. Exogenous ethylene did not influence abscisic acid level. CRE - a cytokinin receptor, increased its expression during maturation in WT and was lower especially at prebreaker in the repressed line and zeatin level was lower at mature green of the repressed line in comparison to WT.ConclusionsIn addition to previously reported effects of MaMADS2 on ethylene, this transcription factor also influences other plant hormones, particularly at the pre-climacteric stage. The cytokinin pathway may play a previously unanticipated role via MaMADS2 in banana ripening. Finally, abscisic acid enhances MaMADS2 expression to promote ripening, but the transcription factor in turn auto inhibits ABA synthesis and signaling. Together, these results demonstrate a complex interaction of plant hormones and banana fruit ripening mediated by MaMADS2.

Effects of growth regulators on reproductive abscission in faba bean (Vicia fabacv. Troy)

SummaryGrowth regulators were applied to faba bean (field bean) plants in order to study hormonal control of premature reproductive abscission. Combined data from pairs of racemes sited in a consistently yielding region of the main stem indicated effects of growth regulator treatments. Decapitation increased pod numbers, but the inhibitory influence of the upper shoot could not be replaced completely by indol-3yl-acetic acid (IAA) applied to the cut stem stump. Blockage of auxin transport through the stem with the auxin-transport inhibitors 2, 3, 5-triiodobenzoic acid (TIBA) or methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (CF, chlorflurenol) reduced pod numbers above the application point. The latter effects might have been indirect and due to elevated ethylene levels, since pod retention in this shoot region was decreased when sprayed with the ethylene-releasing compound 1-aminocyclopropane carboxylic acid (ACC) and increased when sprayed with ethylene-biosynthesis inhibitors 2-aminoethoxyvinyl glycine (AVG) or l-amino-2-cyclopropylcyclopropane carboxylic acid (cyclopropyl-ACC). Pod numbers were increased when the reproductive structures themselves were sprayed with IAA, gibberellic acid (GA3) or 6-benzylaminopurine (BAP), although a corresponding increase in total seed weight occurred only with the latter growth regulator. Application of BAP or abscisic acid (ABA) as root drenches showed that levels of reproductive abscission were raised or lowered with BAP treatment, depending on its concentration, and lowered with ABA treatment. It is suggested that growth regulator treatments leading to decreased ethylene production in the shoot and/or increased cytokinin and abscisic levels in the xylem sap are those most likely to reduce abscission.

Effects of light on somatic embryo development and abscisic levels in carrot suspension cultures

Carrot cells were cultured under various light spectra and intensities at different times following the initiation of suspension cultures from callus. The highest intensity white and blue light treatments were inhibitory to growth and somatic embryogenesis. Red and green light were not different from dark treatments which produced the highest total number of embryoids. After extended time in culture, carrot cells in blue light produced secondary embryoids and anthocyanin. Cultures in red light had multiple cotyledons and orange-pigmented radicles. Leafy cotyledons occurred in all light treatments. Abscisic acid production peaked at the heart stage of embryogenesis and synthesis was most pronounced in blue light. Red light enhanced development to the heart stage. Both the red and blue light spectra may be used to manipulate carrot cell cultures to optimize growth.