H. Greenway

Crop loss due to soil salinization is an increasing threat to agriculture worldwide. This review provides an overview of cellular and physiological mechanisms in plant responses to salt. We place cellular responses in a time- and tissue-dependent context ...Read More

Enzymes which are affected by the addition of inorganic salts during in vitro assay were extracted from salt-sensitive Phaseolus vulgaris, salt-tolerant Atriplex spongiosa, and Salicornia australis and tested for sensitivity to NaCl. In each case malate dehydrogenase, aspartate transaminase, glucose 6-phosphate dehydrogenase, and isocitrate dehydrogenase showed NaCl responses similar to those found for commercially available crystalline enzymes from other organisms. Enzymes extracted from plants grown in saline cultures showed no important changes in specific activity or salt sensitivity. Interaction of pH optima and NaCl concentrations suggests that enzymes may differ in the way they respond to salt treatment.

Abstract The present paper describes the effects of growth of roots of wheat ( Triticum aestivum cv. Gamenya) in hypoxic nutrient solutions on acrenchyma formation and O 2 movement from shoots to roots. Two types of roots were investigated: (1) seminal roots of 4–7‐d‐old seedlings, and (2) seminal and nodal roots of 10–28‐d‐old plants. Gas‐filled porosity of seminal and nodal roots increased from 3 to 12% and from 5–7 to 11–15%, respectively, when the roots emerged in stagnant or N 2 ‐flushed solutions (0.003 mol m −3 O 2 ) compared with growth in continuously acrated solutions (0.26 mol m −3 O 2 ). However, neither root type increased in porosity when they were longer than 100–200 mm at the start of the exposure to these stagnant or N 2 ‐flushed treatments. A vernier microscope and cylindrical platinum‐electrode were used to examine the relationship between root extension and transport of O 2 from shoots to roots via the gas spaces. Measurements were made when the roots were in an anoxic medium and were dependent solely on O 2 supplied from the shoots. For seminal roots of 5–7‐d‐old seedlings raised in stagnant solutions (90–100 mm), internal O 2 transport was sufficient to support a rate of root elongation in the O 2 ‐free medium of between 0.03 and 0.17 mm h −1 . When the O 2 pressure around the shoots was increased from 20 to 100 kPa O 2 , the O 2 concentrations at the walls of the expanding zone (2–7 mm from the tip) of these roots increased from 0.006 mol m −3 to between 0.04 and 0.26 mol m −3 , and the rate of root extension increased five‐fold. Oxygen transport to roots grown continuously in acrated solutions was considerably less than for roots raised in stagnant solutions; this difference was greater for seminal than for nodal roots. When the acrated seminal roots were longer than 100 mm and transferred to an O 2 ‐free root medium, O 2 concentration became zero at the root tip causing elongation to cease. After 24 h of anoxia, none of these roots were able to resume elongation following a return to acrated solutions.

O(2) deficiency during soil waterlogging inhibits respiration in roots, resulting in severe energy deficits. Decreased root-to-shoot ratio and suboptimal functioning of the roots, result in nutrient deficiencies in the shoots. In N(2)-flushed nutrient solutions, wheat seminal roots cease growth, while newly formed adventitious roots develop aerenchyma, and grow, albeit to a restricted length. When reliant on an internal O(2) supply from the shoot, nutrient uptake by adventitious roots was inhibited less than in seminal roots. Epidermal and cortical cells are likely to receive sufficient O(2) for oxidative phosphorylation and ion transport. By contrast, stelar hypoxia-anoxia can develop so that H(+)-ATPases in the xylem parenchyma would be inhibited; the diminished H(+) gradients and depolarized membranes inhibit secondary energy-dependent ion transport and channel conductances. Thus, the presence of two transport steps, one in the epidermis and cortex to accumulate ions from the solution and another in the stele to load ions into the xylem, is important for understanding the inhibitory effects of root zone hypoxia on nutrient acquisition and xylem transport, as well as the regulation of delivery to the shoots of unwanted ions, such as Na(+). Improvement of waterlogging tolerance in wheat will require an increased capacity for root growth, and more efficient root functioning, when in anaerobic media.

Journal Article Effects of Anoxia on Wheat Seedlings: II. INFLUENCE OF O2 SUPPLY PRIOR TO ANOXIA ON TOLERANCE TO ANOXIA, ALCOHOLIC FERMENTATION, AND SUGAR LEVELS Get access I. WATERS, I. WATERS School of Agriculture, University of Western AustraliaNedlands, WA 6009, Australia Search for other works by this author on: Oxford Academic PubMed Google Scholar S. MORRELL, S. MORRELL School of Agriculture, University of Western AustraliaNedlands, WA 6009, Australia Search for other works by this author on: Oxford Academic PubMed Google Scholar H. GREENWAY, H. GREENWAY 1 School of Agriculture, University of Western AustraliaNedlands, WA 6009, Australia 1To whom correspondence should be addressed. Search for other works by this author on: Oxford Academic PubMed Google Scholar T. D. COLMER T. D. COLMER School of Agriculture, University of Western AustraliaNedlands, WA 6009, Australia Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Experimental Botany, Volume 42, Issue 11, November 1991, Pages 1437–1447, https://doi.org/10.1093/jxb/42.11.1437 Published: 01 November 1991 Article history Received: 29 August 1990 Accepted: 03 June 1991 Published: 01 November 1991