Donald Aspinall

Amino acid and glycine betaine accumulation in cold-stressed wheat seedlings

Abstract The changes in amino acid and glycine betaine content in response to cold stress (4°) in wheat seedlings were investigated using HPLC and NMR. Glutamine, proline, 4-aminobutyric acid, alanine, aspartic acid, asparagine, glycine, glycine betaine, valine, threonine and isoleucine levels increased while glutamic acid content decreased. These changes were not accompanied by a reduction in leaf water potential. Possible mechanisms of accumulation of these solutes are discussed.

Effects of temperature and gibberellic acid on 4-desmethylsterol composition of Avena sativa stem segments

Abstract Of the three morphological subunits of Avena sativa stem segments (node, leaf-sheath and internode) examined, internodes constituted the richest source of phospholipids and sterols, yielding almost double the concentration of lipid found in the leaf-sheath. The phospholipid compositions of nodes and internodes were similar, comprising mostly phosphatidylcholine (PC) and phosphatidylethanolamine (PE), with linoleic, linolenic and palmitic acids as the predominant component fatty acids. Leaf-sheath tissue contained mainly PE, with equally high amounts of palmitic, linoleic and linolenic acids. β-Sitosterol and cholesterol were the major 4-desmethylsterols of the internode, while β-sitosterol was predominant in the node and leaf-sheath tissues. The growth temperature of segments prior to isolation produced its major effect on the concentration of stigmasterol, which decreased markedly with temperature. The sitosterol/stigmasterol ratio increased significantly as temperature decreased. Stem segments isolated from plants treated with gibberellic acid (GA 3 ) for 3 weeks, showed a significant reduction in the amounts of 4-desmethyl sterols on a dry wt basis when compared with control segments. However, when stem segments were incubated with GA 3 for 20 hr, no change in 4-desmethylsterol composition or concentration was observed, even though significant growth in response to GA 3 occurred.

Growth and development of roots of grapevine (Vitis vinifera L.) in relation to water uptake from soil.

Developmental patterns of lateral roots and their vascular differentiation were investigated for Vitis vinifera L. cv. Shiraz to assess the likely contribution of lateral roots to total water uptake of plants subjected to different irrigation regimes. Correlation analyses showed a significant positive correlation between main root diameter and the diameter of first order lateral roots of well-watered plants, but in water-stressed plants the two were not significantly correlated. The correlations between diameters of first order lateral roots and the diameters of main roots were greater than correlations between the lengths of first order laterals and the diameters of main roots. The suberised surface area of well-watered main roots increased from 4% of total surface area at 0.25 cm to 100% at 10 cm from the tip, whereas that of stressed plants increased from 15% at 0.25 cm to 100% at 5 cm from the tip. In all treatments the highest linear density of first order laterals was about 7 laterals cm(-1) of main root. More than 50% of first order laterals had diameters less than 0.05 cm, and more than 90% of them had lengths less than 5 cm. Calculations of axial resistances based on xylem diameter measurements suggest that the axial resistances of root segments may not be uniform along roots as is often assumed in models of water uptake. Water flow into the main roots via the lateral root pathway is likely to be much smaller than that via the direct radial flow pathway as only about 1 % of surface area of main roots is directly occupied by lateral roots, leaving the other 99 % of main root surface area available for the direct radial flow pathway.

Vessel-diameter distribution in roots of grapevines (Vitis vinifera L. cv. Shiraz)

The distribution frequency patterns of diameter of xylem vessels and percentage of total predicted axial conductances were studied in 190-day and 212-day-old main roots of grapevine (Vitis vinifera L. cv. Shiraz) grown under well-watered and stressed conditions. The protoxylem were the first to mature and were responsible for most of the theoretical conductance in root segments between the tip and 2.5 cm from the tip. Some large xylem vessels retained cross walls and protoplasm up to 22.5 cm from the tip. Statistical tests using the Kolmogorov-Smirnov two sample test showed that the pattern of distribution frequency of xylem vessels classified in different diameter classes varied with distance from the root tip. The distribution frequency of xylem vessels was similar in both well-watered and stressed plants from the tip up to 15 cm from the tip. At distances further from the tip the distribution frequency of xylem vessels of well-watered plants was significantly different from that of stressed plants, with the former having more larger vessels than the latter. The pattern of vessel distribution frequency was different from that of percent total axial conductance (Kh) predicted with fewer large vessels carrying most of the axial flow.

Effects of temperature and gibberellic acid on phospholipid composition of Avena sativa stem segments

Abstract-Stem segments taken from Auena satiua plants grown at lo”, 20” or 30” varied in their phospholipid composition depending on the growth temperature; as temperature was lowered, there was a shift towards a greater proportion of unsaturated fatty acids. A significant increase was observed in the concentration of linolenic acid (18: 3) as growth temperature was lowered. Although prolonged treatment of oat plants with GA, produced marked changes in phospholipid composition of stem segments, these changes did not always accompany the GA,-induced growth response of segments, Treatment of stem segments with GA, for only 20 hr produced a significant growth response with little or no effect on phospholipid composition over this time. The data support the hypothesis that GAS-induced growth in Avena stem segments can occur without a concomitant change in phospholipid composition. INTRODUCTION The mechanism of action of gibberellic acid (GA,) in plant tissue is still unclear. Some evidence has suggested that the hormone may act by altering either membrane composition [l, 21 or membrane structure [3, 41. Compositional alteration may be brought about by changing the ratios ofphospholipid: sterol: protein, or by replacing individual phospholipids, sterols and proteins with new or different species (e.g. by changing the fatty acid structure of phospholipids, or by changing sterol composition). Work on the barley aleurone system has indicated a possible effect of GA, on enzymes of phospholipid synthesis [5, 61, although more recent studies on wheat aleurone tissue failed to show any control of phospholipid synthesis by GA, [7, 8-j. The