Plant Growth and Development in Molecular Perspective

Abstract

Summary After some false starts in which inactive plant substances were isolated, the isolation and identification of auxin as the growth substance at the meristems and of ethylene as the ripening agent in climacteric fruits represented outstanding achievements. In early work, the non‐localized origin of auxin at the meristem and its possible transport for coleoptile development were obscured by the superimposition on the results of physiological experiments of the idea of a close parallelism between the plant‐growth substances and mammalian hormones. At that time, an absence of chemical instrumentation, suitable for measurement of the tissue levels, compounded the difficulty in interpreting available physiological evidence. Member(s) of each of the five groups of naturally occurring plant‐growth substances, namely the auxins, cytokinins, gibberellins, ethylene and the growth inhibitors, including abscisic acid, are biologically active at a concentration of 10 μm or less, however, and in this respect they would appear to qualify as candidate phytohormones. The sensitivity of plant cells to phytohormones contributes to plant growth and development, and both the variations in sensitivity, for example, of wheat coleoptiles towards growth and the growth of the coleoptiles per se give parallel unimodal relationships with regard to time; the curve representing sensitivity precedes that for growth. A new graphical analysis implies that the growth sensitivity and growth rate functions are mutually interdependent. The assumption is made in point 4 that growth substance complexes with receptor protein in growth‐sensitive cells, and the concept of receptors would provide explanation for the obvious amplification of effects induced by growth substances. Numerous biological situations occur in which the presence of significant amounts of plant hormone controls growth and development. In gravitropism and phototropism, tropistic curvature depends on the difference in physiological concentration of auxin on the two sides of the organ concerned. In infected tobacco plants, the cytokinin to auxin ratios for the tumours determine the kind of development (tumours and shoots, tumours only or tumours plus roots), which takes place. Auxin‐binding protein has been identified immunologically, and isolated. Work with hormone receptors for gibberellin does not afford unequivocal evidence for more than one primary site of action. Hitherto, no specific receptor protein is known for cytokinins. Clear evidence derives, both from structure–activity relationships and from unimodal concentration–response curves, for receptor specificity to auxin action. There is also evidence for a structure–activity relationship in respect of the cytokinin series of compounds. From the evidence (points 1–8), there emerges a picture of hormone‐induced growth and development of plant cells, which have been made sensitive to hormone through the presence of specific receptor proteins. That plant growth and developmental processes involve changes in gene expression...

In vitro high frequency plant regeneration from hypocotyl and root segments of spinach by organogenesis

“…Sasaki (1989) suggested that GA3, by repression of callus proliferation, stimulated shoot formation of spinach hypocotyl tissues. High concentration of auxin stimulated ethylene synthesis (Mackenzie & Street 1970;Hathway 1990), which inhibited or retarded caulogenesis (Pua et al 1990). It was known that spinach tissue cultures were sensitive 243 to ethylene (Dalton & Street 1976), and at the same time, they required a relatively high level of auxin for caulogenesis (cf our results and Sasaki 1989;Mii et al 1992).…”

Systems biology and mechanics of growth

“…This type of axial directional growth leads to elongated or shortened shape in a single direction. In the case of a plant or leaf growth, both nutrient‐driven and genetically programmed growth can be understood as the nonmechanical driver for the growth response . Classical examples in plant physiology including growing rhubarb or curly dock can be modeled using this framework …”

“…In the case of a plant or leaf growth, both nutrient-driven and genetically programmed growth can be understood as the nonmechanical driver for the growth response. 79 Classical examples in plant physiology including growing rhubarb or curly dock can be modeled using this framework. 49,80 Cortex Subcortex FIGURE 5 | Area growth of the cerebral cortex.…”

Changes in cellular macromolecules (DNA, RNA and protein) during seed germination in tomato, following the use of a butenolide, isolated from plant-derived smoke

“…Successful culmination of these cellular events ensures the availability of hydrolytic enzymes participating in the mobilization of stored reserve from the storage organs (cotyledons or endosperm) to the growing embryonic axis. The total protein pool at the seedling stage is represented by both newly synthesized proteins as well as those derived from hydrolysis of reserve seed material (Hathway 1990). …”