John Gorham

VARIATION IN CARBON ISOTOPE DISCRIMINATION AND OTHER TRAITS RELATED TO DROUGHT TOLERANCE IN UPLAND COTTON CULTIVARS UNDER DRYLAND CONDITIONS

Abstract The search for traits related to drought resistance is a main step in the selection of cotton with improved performance under limited water supply. The effect of cultivar and drought conditions on the physiological traits, such as carbon isotope discrimination (Δ), photosynthesis (A), transpiration (E), stomatal conductance (gs), leaf osmotic potential (ψo) and leaf-water content (LWC), were studied in Andalucia, Spain. The morphological traits, such as leaf area and specific leaf weight (SLW), were also evaluated. In the initial study performed with three cotton cultivars, positive associations between Δ and A, E and gs were observed under increasing water stress. The A/gs ratio was negatively associated with Δ, and a strong negative correlation was observed between SLW and Δ. In a further experiment, using a wider group of cultivars, an apparent genotypic variation in Δ was observed in plants after withholding irrigation. Genotypic variation was found for gas exchange (A, E, gs) and leaf variables (LWC, SLW, ψo). No relationship was found between Δ and gas exchange or leaf-related traits. Considering both samplings as situations of different water availability, and plotting the data together, a low but positive correlation was observed between Δ and gs or LWC, and negative between Δ and A/gs. A remarkable correlation between LWC and gas exchange traits was found, whereas SLW was negatively correlated with A, A/E, and LWC. In dryland trials (1996 and 1997), the genotypic variation in LWC was positively associated with Δ. Under these conditions, an association between genotypic variation in Δ and A or A/E was observed. A positive correlation between yield and Δ was detected in 1996. Carbon isotope discrimination might be a useful tool for selecting drought-tolerant cotton genotypes but more studies are required to define more precisely the sampling conditions and the influence of factors affecting Δ and its relationship to crop yield.

Dynamic quantitative trait loci for salt stress components on chromosome 1 of rice

Rice varieties Co39 and Moroberekan differ for leaf Na+ concentrations when grown at moderate salinity (100–150 mol m–3 NaCl; 10 : 1 or 20 : 1 Na+ to Ca2+ ratio). Recombinant inbred lines (RILs) from a cross between them were used to map quantitative trait loci (QTL) under salt stress over several weeks. Two experiments (conducted with 170 and 96 RILs, and a linkage map of 126 RFLP markers) identified a major effect on QTL for leaf Na+ concentration and K+ : Na+ ratio on chromosome 1 in a region corresponding to 11.07–14.6 Mbp. No leaf Cl– QTL were detected. In a third experiment, leaves and sheaths were harvested after 7 and 21 days at 100 mol m–3 NaCl. The linkage map of chromosome 1 was improved by the addition of 28 microsatellite markers, which resolved distinct QTL for Na+ and K+ concentrations, and K+ : Na+ ratio. After 7 days’ stress, the most significant QTL were in the region of 11.56–12.66 Mbp. The highest Na+ concentrations were recorded in the sheaths. Na+ concentration QTL were detected for leaves, but not for sheaths. After 21 days’ stress, the region containing the most significant QTL extended to 11.07 Mbp in leaves and in sheaths. A QTL for the ratio of leaf Na+ to sheath Na+ concentrations was found at 11.39–12.39 Mbp. These findings suggest that multiple genes in this region are involved in the response to salinity, and their impact is dynamic according to stress duration, and leaf age and type.

Glycinebetaine is a major nitrogen-containing solute in the malvaceae

The zwitterionic quaternary ammonium compound glycinebetaine was detected in all but three of over 100 species of various genera in the family Malvaceae. In a more limited range of species, particularly of Gossypium, glycinebetaine accumulated to concentrations sometimes in excess of 100 mM water in response to water deficit or salinity stress. Glycinebetaine concentrations were highest in young tissues and accounted for about 10% of the total nitrogen.

Intra- and Inter-Cellular Compartmentation of Ions

Accumulation of sodium salts by higher plant tissues contributes to osmotic adjustment to increased external salinity. This crude statement masks subtle and varied differences in behaviour between the main intracellular compartments (cell wall, cytoplasm and vacuole), and between cell types. The cytosol, is characterized by a marked selectivity for K+ and HPO 4 − (in P deficient plants), but against Ca++, Na+, Cl−, NO 3 − and H+ and organic acids. These solutes are largely occluded in the vacuole. In hyperosmotic conditions compatible organic solutes accumulate in the cytoplasm to achieve osmotic equilibrium across the tonoplast. Turgor homeostasis is an important component of the plant’s response to salt stress, but this is dependent on the regulation of changes in both the intracellular and cell wall solutes. There are also marked differences in the ions accumulated in vacuoles of leaf epidermal, mesophyll and other cell types that appear to be cell- and species-specific.

Performance of durum wheat landraces in a Mediterranean environment (eastern Sicily)

SummaryThe evaluation aimed at identifying landrace genotypes adapted to the rather unfavourable growing conditions of durum wheat in Sicily, to be used as parental material in a breeding programme. The trial was carried out in three seasons experiencing varying climatic conditions, and included 75 landraces, 25 of which were selected under severe drought in Syria. Wide differences were observed for most traits among genotypes and seasons of evaluation. Yields of the best performing entries identified in each season never significantly differed from that of the best check variety. The top-yielding landraces were consistently better than the remaining entries for the three yield components, viz. number of spikes per plant, number of kernels per spike and mean kernel weight. In the driest season they were also significantly earlier in heading, confirming the importance of earliness under drought. An analytical breeding approach relying on an array of morpho-physiological traits as selection criteria did not seem appropriate for the given environment, as the variable stress level enhanced the importance of specific traits under specific situations. The genotypic response was largely season-specific. Nonetheless, five landraces were in the best group in all seasons. The selection made in Syria also appeared somewhat effective in Sicily, particularly in the less favourable seasons.

Betaine distribution in the Malvaceae

Aerial parts of 26 taxa, distributed in 18 genera and all 5 tribes of the Malvaceae have been examined for the presence of betaines. Glycinebetaine was obtained in high yield (0.5-4.6%, dry weight) from all the plants studied, except Abelmoschus moschatus, in extracts of which glycinebetaine was not detected. Trigonelline was recorded for 16 of the plants tested, but the yields were low (0.005-0.07%, dry weight). Roots and flowers of a few of the species were also examined for betaines. The same compounds as those found in the aerial parts were usually detected, but the glycinebetaine contents of the roots and flowers were considerably lower.

Inhibition of photosynthesis by stilbenoids

Abstract The effects of a number of naturally occurring and synthetic stilbenes on photosynthetic functions in isolated chloroplasts of Spinacia oleracea were investigated. CO 2 -dependent O 2 evolution and electron flow from water to methylviologen in uncoupled chloroplasts were inhibited by all the compounds tested. Uncoupling of electron transport and photophosphorylation were also observed. Electron flow from DCPIPH 2 to methylviologen showed the superimposed effects of uncoupling and inhibition, the overall effect depending on the concentration of the stilbene. Pinosylvin and its methyl ethers were among the most inhibitory of the compounds tested. The implications of these findings are discussed in terms of the growth regulatory and antifungal activities of stilbenoids.

Genetics of Salinity Responses and Plant Breeding

Molecular biology offers the possibility of designing new plant genotypes with enhanced resistance to salinity. This does not, however, mean that understanding the genetics and physiology of responses to salinity is complete or no longer necessary. To be able to exploit the new technologies it is important to understand the inheritance of traits and how they can be integrated in complex, highly structured whole plants through varying phases of development. In this chapter we consider the constraints and possibilities of breeding crops for salt resistance from the viewpoint of the different disciplines of agronomy, breeding, physiology and molecular biology.