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  • Author or Editor: Andrew D. Hanson x
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Abstract

Climatic factors-particularly the ranges and mean values of water availability and temperature-were major selective forces in the evolution of crop plants, and it is adaptation to these factors which sets the broad distribution limits for today's crops. The extremes of the ranges of water availability and temperature (the stresses of drought, flooding, cold and heat) likely to be encountered at any location are particularly important in determining the crop species and cultivars which can be profitably grown there, i.e. the adapted genotypes for that environment. The phenomenon of plant adaptation to environment can, in principle, be understood in physiological, biochemical and genetic terms. Current research on crop adaptation to stress-prone environments, research which seeks such an understanding, may influence the future practices in both plant breeding and crop management.

Open Access

Proline and various betaines can function as osmoprotectants and cryoprotectants when accumulated in the cytoplasm of cells. Genetic engineering can raise levels of these compounds and thereby improve stress resistance; Citrus species are potential candidates for this. Before attempting such engineering, it is necessary to characterize the natural osmoprotectants of Citrus and related genera. We therefore surveyed 55 cultivated and wild species of the Aurantioideae, analyzing proline and betaines in leaves of mature trees. Some citrus relatives accumulated proline alone; others accumulated proline and proline betaine, as did all Citrus species studied. The levels of these two compounds ranged from about 20 to 100 μmol·g-1 dry mass, and were significantly inversely correlated. Proline betaine is known to be synthesized from proline and to be a better osmoprotectant. Because Citrus species all have more proline than proline betaine, there is scope for engineering more of the latter. Many species had small amounts of hydroxyproline betaine; other betaines were essentially absent. The lack of other betaines means that it would also be rational to engineer the accumulation of glycine betaine or similar compounds.

Free access

Abstract

Overall plant resistance to environmental stresses is conferred by characters expressed at four levels of organization: developmental, structural, physiological, and metabolic or biochemical (Fig. 1). Characters expressed at the upper levels are usually controlled by many genes. The potential for using recombinant DNA (rDNA) technology to understand and alter stress resistance is presently limited to single-gene traits, especially those expressed at the biochemical level. Such traits may be rare, and the effects on overall crop performance of modifying them cannot be foretold (Fig. 1), but they remain invaluable for basic research. The ability to construct specific mutations in vitro with cloned genes, and then to reintroduce them into the plant via some mechanism of transformation, would provide the power of genetic analysis to test models of molecular function in stress (2, 22). The ability to suppress expression of individual genes by the use of anti-sense messages would serve similar ends (4, 25). Thus, there is much interest in identifying and isolating single genes related to stress resistance or susceptibility. We discuss and criticize three ways of going about this task and show how helpful an understanding of stress physiology and biochemistry can be.

Open Access

Like everything for the past 2 centuries, agriculture has depended increasingly on fossil fuel energy. Pressures to shift to renewable energy and changes in the fossil fuel industry are set to massively alter the energy landscape over the next 30 years. Two near-certainties are increased overall prices and/or decreased stability of energy supplies. The impacts of these upheavals on specialty crop production and consumption are unknowable in detail but the grand lines of what will likely change can be foreseen. This foresight can guide the research, extension, and teaching needed to successfully navigate a future very unlike the recent past. Major variables that will influence outcomes include energy use in fertilizer manufacture, in farm operations, and in haulage to centers of consumption. Taking six increasingly popular fruit and vegetable crops and the top two horticultural production states as examples, here we use simple proxies for the energy requirements (in gigajoules per ton of produce) of fertilizer, farm operations, and truck transport from Florida or California to New York to compare the relative sizes of these requirements. Trucking from California is the largest energy requirement in all cases, and three times larger than from Florida. As these energy requirements themselves are all fairly fixed, but in future will likely rise in price and/or be subject to interruptions and shortages, this pilot study points to two commonsense inferences: First, that fruit and vegetable production and consumption are set to reposition to more local/regional and seasonal patterns due to increasing expenses associated with fuel, and second, that coast-to-coast produce shipment by truck will become increasingly expensive and difficult.

Open Access