Hirohumi Saneoka

Salt Tolerance of Glycinebetaine-Deficient and -Containing Maize Lines.

Pairs of homozygous near-isogenic glycinebetaine-containing (Bet1/Bet1) and -deficient (bet1/bet1) F8 lines of Zea mays L. (maize) were tested for differences in salt (150 mM NaCl or 127.25 mM NaCl plus 22.5 mM CaCl2) tolerance. The Bet1/Bet1 lines exhibited less shoot growth inhibition (as measured by dry matter accumulation, leaf area expansion rate and/or, plant height extension rate) under salinized conditions in comparison to their nearisogenic bet1/bet1 sister lines. These growth differences were associated with maintenance of a significantly higher leaf relative water content, a higher rate of carbon assimilation, and a greater turgor in Bet1/Bet1 lines than in bet1/bet1 lines under salinized conditions. These results strongly suggest that a single gene conferring glycinebetaine accumulation (and/or a tightly linked locus) plays a key role in osmotic adjustment in maize.

Betaine Aldehyde Dehydrogenase in Sorghum (Molecular Cloning and Expression of Two Related Genes)

The ability to synthesize and accumulate glycine betaine is wide-spread among angiosperms and is thought to contribute to salt and drought tolerance. In plants glycine betaine is synthesized by the two-step oxidation of choline via the intermediate betaine aldehyde, catalyzed by choline monooxygenase and betaine aldehyde dehydrogenase (BADH). Two sorghum (Sorghum bicolor) cDNA clones, BADH1 and BADH15, putatively encoding betaine aldehyde dehydrogenase were isolated and characterized. BADH1 is a truncated cDNA of 1391 bp. BADH15 is a full-length cDNA clone, 1812 bp in length, predicted to encode a protein of 53.6 kD. The predicted amino acid sequences of BADH1 and BADH15 share significant homology with other plant BADHs. The effects of water deficit on BADH mRNA expression, leaf water relations, and glycine betaine accumulation were investigated in leaves of preflowering sorghum plants. BADH1 and BADH15 mRNA were both induced by water deficit and their expression coincided with the observed glycine betaine accumulation. During the course of 17 d, the leaf water potential in stressed sorghum plants reached -2.3 MPa. In response to water deficit, glycine betaine levels increased 26-fold and proline levels increased 108-fold. In severely stressed plants, proline accounted for >60% of the total free amino acid pool. Accumulation of these compatible solutes significantly contributed to osmotic potential and allowed a maximal osmotic adjustment of 0.405 MPa.

Cell membrane stability, an indicator of drought tolerance, as affected by applied nitrogen in soyabean

Four soyabean cultivars were grown with two N application rates (50 and 300 kg N/ha) in the field at Hiroshima University, Japan, from June to August 1988. Cell membrane stability (CMS) by the polyethylene glycol (PEG) test, leaf water relations and nutrient concentrations in cell sap and leaf tissues were measured when the plants were 50 days old, in the uppermost fully expanded leaves. Cell membrane stability was higher at the higher N rate, the increase over the lower rate being greater in the cultivars Lee+ and Lee–than in Tamahomare and T201. Leaf water potential was not affected by the higher rate of N application. Osmotic adjustment, which was independent of water stress, was observed with the higher rate of N and it was higher in Lee + and Lee–than in Tamahomare and T201. It is suggested that osmotic potential in leaf tissues may influence CMS measured by the PEG test. Solute concentrations in cell sap and leaf tissues were higher at the higher N rate. Sugar and K were the major contributors to osmotic potential.

Near-Isogenic Lines of Maize Differing for Glycinebetaine

A series of near-isogenic glycinebetaine-containing and -deficient F8 pairs of Zea mays L. (maize) lines were developed. The pairs of lines differ for alternative alleles of a single locus; the wild-type allele conferring glycinebetaine accumulation is designated Bet1 and the mutant (recessive) allele is designated bet1. The near-isogenic lines were used to investigate whether glycinebetaine deficiency affects the pool size of the glycinebetaine precursor, choline, using a new method for glycinebetaine and choline determination: stable isotope dilution plasma desorption mass spectrometry. Glycinebetaine deficiency in maize was associated with a significant expansion of the free choline pool, but the difference in choline pool size was not equal to the difference in glycinebetaine pool size, suggesting that choline must down-regulate its own synthesis. Consistent with this, glycinebetaine deficiency was also associated with the accumulation of the choline precursor, serine. A randomly amplified polymorphic DNA marker was identified that detects the bet1 allele. In 62 F8 families tested the 10-mer primer 5[prime]-GTCCTCGTAG produced a 1.2-kb polymerase chain reaction product only when DNA from Bet1/bet1 or bet1/bet1 lines was used as template. All 26 homozygous Bet1/Bet1 F8 families tested were null for this marker.

Cell membrane stability and leaf water relations as affected by nitrogen nutrition under water stress in maize

Abstract A field experiment was conducted to investigate the effect of N nutrition under water stress conditions on the cell membrane stability (CMS) measured by the polyethylene glycol (PEG) test, plant water relations, and osmotic adjustment in maize (Zea mays L.). Stressed plants showed greater adaptations to water deficits at higher N levels. Leaf water potential and osmotic potential decreased, turgor potential increased, and CMS increased with increasing N levels. Osmoregulation was evident at higher N levels with sugar and K as the major osmotic contributors. Results suggest that osmoregulation is influenced by N nutrition.

Relationship between Water use Efficiency and Cuticular Wax Deposition in Warm Season Forage Crops Grown under Water Deficit Conditions

In order to clarify the relationship between water use efficiency (apparent photosynthetic rate/transpiration rate) and the synthesis and deposition of epicuticular wax and of lipids in leaf internal tissues in various forage crops with different drought tolerance, the contribution of cuticular wax to the leaf cuticular resistance to water loss under water stress was estimated. Under water stress conditions, the cuticular resistance of the drought tolerant plant Chloris gayana Kunth. increased about twofold compared with that of a well-watered plant, whereas the cuticular resistance of the sensitive plant Coix lacryma-jobi L. increased by about 10%. The amount of epicuticular wax deposited on the leaf surface in both plants increased by water stress. However, the amount in the tolerant plant was much higher than those in the sensitive one. Radioactivity of 14C incorporated into the leaf surface wax of stressed C. gayana and C. lacryma-jobi plants was 27 and 50% less than that of well-watered plants, respe...

Responses of Relative Growth Rate, Water Relations and Solute Accumulation to Increasing Water Deficits in Maize

Summary A field experiment was conducted with water stress treatment and well-watered controls using eight maize ( Zea mays L. ) cultivars. Stress treatment was commenced when the plants were 40-d old by withholding water. Growth parameters were measured at the beginning of the treatment and 10 and 20 days after treatment. Leaf water potential, osmotic potential and solute concentration in cell sap were measured at 10 and 20 days after treatment. The root exudation rate was measured on the 22nd day of treatment. A wide range of differences in growth under increasing water deficits was observed between cultivars. Drought-tolerant cultivars maintained turgor by decreasing osmotic potential at low leaf water potentials and they showed higher osmotic adjustment. Sugar and K were the major osmotic contributors. Sugar played a major role in increasing osmotic concentration under water deficit conditions. The root exudation rate was higher in drought-tolerant cultivars under stress.

Effect of phosphorus on drought tolerance in Chloris gayana Kunth and Coix lacryma-jobi L

Abstract In order to evaluate the role of phosphorus (P) nutrition on the drought tolerance of warm season forage crops, i.e. Rhodesgrass (Chloris gayana Kunth) and Jobs tears (Coix lacryma-jobi L. var.ma-yuen Stapf.) which are considered to be the most and the least tolerant species to water stress, respectively, the crops were subjected to water stress at two P nutrition levels. Leaf water potential (ψ i), stomatal resistance (γ s), leaf area, shoot and root dry weight, root development, and photosynthetic rate (P o) were recorded. Shoot and root dry weights decreased at the lower P level and under water stress in both species. Total leaf area per plant decreased by stress and it was smaller at the lower P level than at the higher P level in both species under stress conditions. The root development of both species was markedly inhibited by water stress. In rhodesgrass, total root length and root surface area at the higher P level were 2.3 and 1.7 times larger than those at the lower P level, respectiv...

Evaluation of polyethylene glycol test for measurement of cell membrane stability in maize.

Cell membrane stability (CMS) of three maize (Zea mays L.) cultivars was determined by the polyethylene glycol (PEG) test at different leaf positions and compared with other physiological measurements to clarify the mechanism of the PEG test. Percentage injury in the PEG test was well correlated with the leaf water potential, osmotic potential, leaf thickness, and Ca and Mg concentrations in the leaf tissues and cell sap. It was comparable with the cuticular resistance but did not show any relationship with stomatal resistance. Osmotic potential of leaf tissues may affect the desiccation treatment in the PEG solution. Sugars, K, and Ca were the major contributors to the osmotic potential. Relative contribution of K to the osmotic concentration was higher than that of sugars in maize. Percentage injury in the PEG test was influenced mainly by the osmotic potential, leaf thickness, and Ca and Mg concentrations of leaf tissues.

Seasonal changes in leaf water relations and cell membrane stability in orchardgrass ( Dactylis glomerata)

Fifteen cultivars of orchardgrass (Dactylis glomerata L.) were grown in the field at Hiroshima University, Japan, to investigate seasonal changes in leaf water relations and cell membrane stability (CMS) measured by the polyethylene glycol (PEG) test. Leaf water potential and osmotic potential were measured from August 1988 to August 1989. Solute concentration in leaf cell sap was also estimated. Cell membrane stability increased, leaf water potential and osmotic potential decreased and turgor potential increased with decreasing environmental temperatures during autumn and winter. The significant increases observed in CMS may enable plants to tolerate freezing temperatures during winter (.)