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Summary A morphological and developmental framework is presented for the cellular events leading to graft formation in tomato autografts based on scanning and transmission electron microscopy. Initial adhesion in the pith of grafts is followed by confrontation of new cells generated from the peripheral tissue of stock and scion. Pectinaceous beads on the surfaces of these cells establish a mechanical union between the cell surfaces, forming the functional equivalent of a middle lamella, Plasmodesmata formed de novo at the point of contact between opposing cells link the cell membranes, forming a potential pathway of communication of high specificity. Subsequently, wound vessels differentiate within the ‘callus’ at the graft union, and are connected into the vascular system of stock and scion by wound vessels differentiating from vascular and cortical parenchyma. The significance of these cellular interactions is discussed.

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summary This review attempts to present an overall strategy for the production of useful secondary metabolites by cultured plant cells. After consideration of the nature and utility of secondary metabolites and the possible role of these substances to the plant, the review focuses attention on the properties of the plant cells in culture and how the cell populations and their physical and chemical environment can be manipulated to encourage the synthesis and accumulation of secondary products. Finally, consideration is given to the involvement of genetic engineering in the production of cells to perform particular metabolic tasks and how these techniques might contribute to the development of a new strategy to enable the production of useful secondary metabolites on a commercial scale.

There is a paucity of data regarding developmental changes in trees. Measurements of length, width, length/width ratio, perimeter/width and width/height ratios of tranverse sections, projected and total surface areas, dry weight, specific leaf area and the weight of epicuticular waxes per unit leaf area were made on needles sampled from the uppermost whorl of Sitka spruce trees aged 3, 5, 10, 15, 20 and 38 years. All characteristics, except needle length and the weight of epicuticular waxes, showed asymptotic changes with age that could adequately be described by the Gompertz growth function, and offer potential as indices of physiological age. Asymptotes were reached at different ages (width and the length/width ratio having the slowest rates of change and the perimeter/width ratio, specific leaf area, and the width/height ratio having the fastest) suggesting a predictable sequence of changes. The observed changes in needle morphology are interpreted as a transition from shade to sun leaves.

A novel method is described in which the two halves of an explanted internode of Lycopersicon esculentum. Datura stramonium or Nicandra physaloides may be grafted together successfully in sterile culture. An absolute requirement for the formation of a successful graft is tbe application of indole-3-acetic acid (IAA at 0-2 to 2-0 mg 1~' ) to the apical end of the internode. Tbe addition of kinetin (0 2 mg 1"') to the culture medium stimulated graft development but gibberellic acid (GAj at 0-5 mg 1~*) was inhibitory. Tbe development of tbe graft as measured by an increase in mechanical strength and the formation of vascular connections was similar to tbat observed in whole plant grafts; however, fewer differentiated wound vessel members (WVMs) were detected. This technique should provide a powerful tool for the further study of graft development in compatible and incompatible combinations.

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Cells of Capsicum frutescens Mill. cv. annuum, immobilised in reticulate polyurethane foam, produced higher yields of capsaicin, the pungent principle of Chilli pepper fruits, than did freely-suspended cells, when batch-cultured in a medium conducive to culture growth. In the absence of specific precursors to capsaicin, immobilised cells produced between two and three orders of magnitude higher yields than did suspended cells over 5-d or 10-d culture periods (typically up to 4 or 5 mg capsaicin g(-1) dry weight l(-1) medium compared with up to 30 μg g(-1)l(-1), respectively). These results were reflected by an increased rate and extent of incorporation of L-[U-(14)C]phenylalanine into capsaicin in immobilised as compared with freely-suspended cells, and evidence is presented for an inverse relationship between incorporation of [(14)C]phenylalanine into protein and capsaicin. The accumulation of capsaicin can be experimentally manipulated and increased by supplementing the medium with precursors of capsaicin such as phenylalanine and isocapric acid and by reducing the growth rate of immobilised cells by omitting growth regulators from the medium. The importance of these observations is discussed.