THE CONTRASTING RESPONSE TO SIMULATED ACID RAIN OF LEAVES AND COTYLEDONS OF CABBAGE (BRASSICA OLERACEA L.)

Abstract

SUMMARYBrassica oleracea L. (cabbage) was grown in glasshouse and controlled environments and exposed to simulated rains delivered as sprays at pH 5-6-2-8. A single rain treatment of pH 30 given to lOd old plants elicited a marked downward curvature in the cotyledons, occurring within the duration of the 30-min spray. Subsequent to this initial response, the cotyledon surface was extensively damaged. In contrast, the older 'true' leaves showed little or no injury after similar treatments. Estimates of the contact angles between rain droplets and leaf surfaces, and SEM studies of adaxial surfaces, indicated that the contrasting morphology of the epicuticular wax on cotyledons and leaves was a major factor determining the extent of acid rain damage. Simulated rain treatments of pH 32 and 28, starting at the cotyledons stage, reduced plant growth by 17 and 15% respectively over a 20 d period. However, the same treatments given at later stages in development when the ' true' leaves were predoininant, had no significant effect on growth. In the natural environment the occurrence of rate, highly acidic rain events during different stages of plant development may be an important determinant of the impact of rainfall on vegetation. The young, seedling stage of species, such as B. oleracea, in which cotyledons show poor development of surface wax, may be particularly vulnerable.

Effects of Simulated Acid Rain on Production, Morphology and Composition of Epicuticular Wax and on Cuticular Membrane Development

“…Youngest and oldest leaves are least affected by simulated acid rain (Evans, Gmur & Da Costa, 1978), whilst cotyledons are most affected (Caporn & Hutchinson, 1986). The data presented here are from leaves of intermediate sensitivity.…”

“…Although histological changes and leaf surface modifications induced by simulated acid rain have been investigated (Evans, Gmur & Da Costa, 1977;Evans & Curry, 1979;Adams, Dengler & Hutchinson, 1984;Caporn & Hutchinson, 1986;Crang & McQuattie, 1986), there have been no studies of effects on the cuticle itself. In this paper, the effects of simulated acid rain on production, morphology, composition and regeneration of epicuticular wax and on development of the cuticular membrane in four crop species are described.…”

The use of ion‐selective microelectrodes for measuring calcium and hydrogen ion transfer between foliar surfaces and simulated rain solutions

“…Previously, methods have utilized an unconfined, sessile droplet resident on the foliar surface w'ith: (1) the droplet's application and subsequent removal for chemical analysis; (2) the placing of the tip of a minicombination or conventional ion-selective electrode in contact with the droplet; or, (3) the insertion of the tip of a (pH-sensitive glass) microelectrode into the droplet (Lepp & Dickinson, 1976;Adams & Hutchinson, 1984;Evans, Santucci & Patti, 1985;Caporn & Hutchinson, 1986;Adams & Hutchinson, 1987;Musselman, 1988). These methods have several liabilities (Schonherr & Riederer, 1989), such as evaporation from the surface of the droplet and incomplete or variable mixing within it due to deformation, vibration, or convection.…”

Crystal occurrence and wax disruption on leaf surfaces of cabbage treated with simulated acid rain

“…In an SEM study initiated in our laboratory to examine whether differences in surface features of cotyledons and leaves of cabbage (Brassica oleracea) could account for the much greater sensitivity of the cotyledons of this plant to injury by acid rain (Caporn & Hutchinson, 1986), we observed significant cbanges in the epicuticular waxes on both cotyledons and leaves after a single, short (30 min) exposure to simulated rain of pH 3(). Based on tbis unexpected observation of damage to epicuticular waxes we decided to use cabbage as a model system to test the effect of acidic rain solutions on crystalline waxes.…”