Light-independent accumulation of chlorophyll a and b and protochlorophyllide in green barley (Hordeum vulgare)

Barley ( Hordeum vulgare L. cvs Clipper, Procter, Astrix) seedlings were transferred from daylight to darkness and changes in chlorophyll a , chlorophyll b , protochlorophyllide and chlorophyllide (μ leaf⁻¹) in either the first or second leaf determined spectrophotometrically after separating the esterified from unesterified pigments by partitioning between ammoniacal acetone and light petroleum ether. Chlorophyll a and b as well as protochlorophyllide accumulated in the dark. The ratio of chlorophyll to protochlorophyllide formed in the absence of light was 18:1. 5-aminolevulinic acid (10 m M ) promoted the synthesis of chlorophyll a and b and protochlorophyllide. Pigment synthesis and response to 5-aminolevulinic acid addition was related to tissue age. Mature tissue in the apical third of the leaf accumulated most chlorophyll, but per μg chlorophyll present at the time of transfer to darkness, was less efficient than immature tissue towards the base of the leaf. Immature tissue was also most responsive to added 5-aminolevulinic acid. Chlorophyll synthesis in the dark was accompanied by chloroplast development. Chloroplasts in immature leaf tissue increased in size and extent of thylakoid development when transferred from daylight to darkness. The results indicate that chlorophyll synthesis and chloroplast membrane development in light-grown barley continue into the dark phase of the diurnal cycle. A light-independent protochlorophyllide reductase in light-grown barley seedlings is postulated.     

Indole acetic acid (IAA) induced changes in growth, relative water contents and gas exchange attributes of barley (Hordeum vulgare L.) grown under water stress conditions

Effect of different concentrations of indole acetic acid (IAA) under varying soil water deficit conditions on two barley cultivars viz. B-99094 and Jau-87 was investigated in soil filled earthen pots. There were six treatments including control each with four replicates. Three concentrations of IAA (0, 15 and 30 mg l⁻¹) were applied as foliar spray 30 days after germination. After hormone application, half of the pots were subjected to one cycle of water stress (withholding of water till incipient wilting), followed by regular watering. Plant height, photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency relative water content, dry biomass, and grain yield/plant were significantly reduced by water stress. However, IAA treatments alleviated the adverse effect of water stress and successful in enhancing the plant growth and yield of barley cultivars. Barley cultivar Jau-87 performed better than B-99094. IAA application␣was effective in enhancing growth and photosynthetic efficiency of barley both under normal and water stress conditions.     

Structure,expression and localization of a germin-like protein in barley (Hordeum vulgare L.) that is insolubilized in stressed leaves

The primary leaves of young barley seedlings contain two major, extracellular, acid-soluble proteins of ca. 22 and 23 kDa apparent molecular mass. These proteins disappeared from the intercellular washing fluid upon stress treatments that enhanced H₂O₂ levels and that induced resistance to subsequent challenge by the powdery mildew fungus Erysiphe graminis f. sp. hordei. A partial peptide sequence of the 22 kDa protein was determined, and a cDNA clone was isolated. The 22 kDa protein belongs the the group of germin-like proteins (GLPs) and was designated HvGLP1. Despite its similarity to germin, i.e. oxalate oxidase, no oxalate oxidase activity of HvGLP1 could be detected. The RNA and soluble protein of HvGLP1 was highly abundant in young leaves, less abundant in older leaves and absent in roots. HvGLP1 RNA oscillated with a circadian rhythm, the minimum and maximum of RNA abundance being at the end of the dark and light periods, respectively. Heat and H₂O₂ treatment as well as pathogen infection caused disappearance of HvGLP1 protein from the fraction of soluble proteins of the intercellular space. HvGLP1 protein could be re-solubilized from cell walls of heat- or H₂O₂-treated leaves by boiling in SDS suggesting non-covalent cross linking. Although a physiological role of HvGLP1 insolubilization is still open, the protein may serve as marker for oxidative stress in cereals.     

Effects of light on the catabolism of [2-14C]-3-indole acetic acid in protoplasts, a chloroplast-rich fraction, and a crude cytoplasmic preparation from barley (Hordeum vulgare L)

Abstract. Combined gas chromatography-mass spectrometry has been used to identify 3-indole acetic acid in an extract from protoplasts of barley. In addition, a study has been made of the effect of light on the rate of catabolism of [2-¹⁴C]-3-indole acetic acid by protoplasts, a chloroplast-rich fraction and a crude cytoplasmic preparation from barley leaves. While light enhanced the rate of catabolism of [2-¹⁴C]-3-indok acetic acid by protoplasts and, to a lesser degree, by the chloroplast-rich fraction, it did not affect the catabolic activity of the crude, cytoplasmic fraction. These findings, when considered along with the data of Sandberg, Jensen & Crozier (1983), imply that the rate of turnover of 3-indole acetic acid, in both protoplasts and chloroplasts, is more rapid in light than it is in darkness.