The Role of Phytohormones (Cytokinins) in Chloroplast Development
TL;DR: Although indications are presented that the promotion of chloroplast development by cytokinins is closely connected with a stimulation of the gene expression program for plastogenesis, other sites of hormone action cannot be excluded and are discussed in the last part of the review.
About: This article is published in Biochemie und Physiologie der Pflanzen.The article was published on 1979-01-01. It has received 139 citations till now.
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19 Oct 1987
TL;DR: Plant hormones are a group of naturally occurring, organic substances which influence physiological processes at low concentrations, mainly of growth, differentiation and development, though other processes, such as stomatal movement, may also be affected.
Abstract: Plant hormones are a group of naturally occurring, organic substances which influence physiological processes at low concentrations. The processes influenced consist mainly of growth, differentiation and development, though other processes, such as stomatal movement, may also be affected. Plant hormones1 have also been referred to as ‘phytohormones’ though this term is infrequently used.
1,067 citations
01 Jan 1987
TL;DR: In this article, the authors present a collection of newly written, integrated, illustrated reviews describing their knowledge of plant hormones and the experimental work which is the foundation of this knowledge, which is intended to serve as a text and guide to the literature for graduate level courses in the plant hormones.
Abstract: Plant hormones playa crucial role in controlling the way in which plants grow and develop. While metabolism provides the power and building blocks for plant life it is the hormones that regulate the speed of growth of the individual parts and integrate these parts to produce the form that we recognize as a plant. In addition, they playa controlling role in the processes of reproduction. This book is a description of these natural chemicals: how they are synthesized and metabolized; how they work; how we measure them; and a description of some of the roles they play in regulating plant growth and development. This is not a conference proceedings but a selected collection of newly written, integrated, illustrated reviews describing our knowledge of plant hormones and the experimental work which is the foundation of this knowledge. The information in these pages is directed at advanced students and professionals in the plant sciences: botanists, biochemists, molecular biologists, or those in the horticultural, agricultural and forestry sciences. It is intended that the book should serve as a text and guide to the literature for graduate level courses in the plant hormones, or as a part of courses in plant or comparative development. Scientists in other disciplines who wish to know more about the plant hormones and their role in plants should also find this volume invaluable It is hoped that anyone with a reasonable scientific background can find valuable information in this book expounded in an understandable fashion.
684 citations
TL;DR: Arabidopsis thaliana plants treated with exogenous cytokinins accumulate anthocyanin pigments and it is shown that PAL1, CHS, CHI, and DFR mRNA levels fluctuate during a 24-h period and appear to be controlled by a circadian clock.
Abstract: Arabidopsis thaliana plants treated with exogenous cytokinins accumulate anthocyanin pigments. We have characterized this response because it is potentially useful as a genetic marker for cytokinin responsiveness. Levels of mRNAs for four genes of the anthocyanin biosynthesis pathway, phenylalanine ammonia lyase 1 (PAL1), chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR) were shown to increase coordinately in response to benzyladenine (BA). However, nuclear run-on transcription experiments suggested that although CHS and DFR are controlled by BA at the transcriptional level, PAL1 and CHI are controlled by BA posttranscriptionally. CHS mRNA levels increased within 2 h of BA spray application, and peaked by 3 h. Levels of PAL1 mRNA did not increase within 6 h of BA spray. We also showed that PAL1, CHS, CHI, and DFR mRNA levels fluctuate during a 24-h period and appear to be controlled by a circadian clock. The relation between cytokinin regulation and light regulation of CHS gene transcription is discussed.
262 citations
01 Jan 1987
TL;DR: In this article, the involvement of plant hormones as natural regulators of partitioning of photoassimilates especially to developing seeds is discussed, and it is shown that endogenous plant hormones may serve as modulators of many of the specific rate limiting components.
Abstract: The movement of photoassimilates from sites of synthesis in leaf tissue (source) to the sites of net accumulation in a different tissue (sink) potentially can be regulated at numerous points. Regulation of the net flow of photoassimilates is an integrated process. It is generally accepted that the concentration gradient of photoassimilates between the source and sink is the primary determinant of the current rate of transport and pattern of partitioning (14, 19, 60). However, close examination of the various components involved in the overall process of partitioning indicates that endogenous plant hormones may serve as modulators of many of the specific rate limiting components. This chapter will focus on the involvement of plant hormones as natural regulators of partitioning of photoassimilates especially to developing seeds.
234 citations
TL;DR: Application of benzyladenine to heat-stressed, growth-chamber-grown plants increased thermotolerance in part by reducing kernel abortion at the tip and middle positions on the ear by confirming that shift in hormone balance of kernels is one mechanism by which heat stress disrupts maize kernel development.
Abstract: Temperature stress during kernel development affects maize (Zea mays L.) grain growth and yield stability. Maize kernels (hybrid A619 x W64A) were cultured in vitro at 3 d after pollination and either maintained at 25[deg]C or transferred to 35[deg]C for 4 or 8 d, then returned to 25[deg]C until physiological maturity. Kernel fresh and dry matter accumulation was severely disrupted by the long-term heat stress (8 d at 35[deg]C) and did not recover when transferred back to 25[deg]C, resulting in abortion of 97% of the kernels. Kernels exposed to 35[deg]C for 4 d (short-term heat stress) exhibited a recovery in kernel growth and water content at about 18 d after pollination and kernel abortion was reduced to about 23%. During the cell division phase, abscisic acid (ABA) levels showed a steady decline in the control but maintained a moderate level in the heat-stressed kernels. However, later in development heat-stressed kernels had significantly higher levels of ABA than the control. Cytokinin analysis confirmed a peak in zeatin riboside and zeatin levels in control kernels at 10 to 12d after pollination. In contrast, kernels subjected to 4 d of heat stress had no detectable levels of zeatin and the zeatin riboside peak was reduced by 70% and delayed until 18 d after pollination. The long-term heat-stressed kernels showed low to nondetectable levels of either zeatin riboside or zeatin. Regression analysis of ABA level against cytokinin level during the endosperm cell division phase revealed a highly significant negative correlation in nonstressed kernels but no correlation in kernels exposed to short-term or long-term heat stress. Application of benzyladenine to heat-stressed, growth-chamber-grown plants increased thermotolerance in part by reducing kernel abortion at the tip and middle positions on the ear. These results confirm that shift in hormone balance of kernels is one mechanism by which heat stress disrupts maize kernel development. The maintenance of high levels of cytokinins in the kernels during heat stress appears to be important in increasing thermotolerance and providing yield stability of maize.
218 citations
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467 citations
TL;DR: It is deduced that the signal hypothesis does not apply to chloroplasts; an envelope carrier mechanism is proposed.
Abstract: The small subunit of the chloroplast enzyme ribulose bisphosphate carboxylase is synthesised as a precursor of higher molecular weight when poly A–mRNA from pea cytoplasmic polysomes is translated by wheat-germ ribosomes. This precursor is taken up into intact isolated chloroplasts, and cleaved to its final size in the absence of protein synthesis. It is deduced that the signal hypothesis does not apply to chloroplasts; an envelope carrier mechanism is proposed.
406 citations
TL;DR: During the last 4 years, several chemical substances have been shown to retard senescence of leaf blades, and in this respect the compounds would atppear to substitute either directly or indirectly for the unknown so-called root factors.
Abstract: The chemical changes that occur in leaves as they grow old have been well characterized for many species. The endogenous factors which control and regulate these changes in plant cells remain, to a great extent, obscure, and the problem of why the cell eventually dies is yet unsolved. A normal feature of the ageing leaf blade is a continuous decline in protein level (1). The most rapid fall occurs during senescence and is associated with irreversible yellowing, loss of chlorophyll, and the eventual death of the organ. When a mature leaf is excised from the plant and the petiole kept in water, these same symptoms of senescence occur and, provided the petiole does not form roots, the protein content of the blade may fall to less than half the original value within a few days. If, however, the petiole forms roots, the behavior of the excised leaf is quite different. It will remain green and photosynthetically active, increasing in dry weight and total protein for periods extending, in some cases, to several years (2), much longer, in fact, than the leaf would survive in situ. The factors responsible for senescence and the decline of total protein in the leaf are not fully understood. Experiments with excised leaves have shown that the decrease in protein content of the blade is not necessarily due to a lack of carbohydrate, nitrogen, or other nutrients (14, 4) or to an inability of the cells themselves to synthesize amino acids (13) but is due, rather, to a failing ability to incorporate these amino acids into protein (11). Provided the leaf has a growing root system, the incorporation of amino acids proceeds normally, and it seems logical to assume that the roots metabolize and supply the blade with certain factors necessary for the continued synthesis of protein. During the last 4 years, several chemical substances have been shown to retard senescence of leaf blades, and in this respect the compounds would atppear to substitute either directly or indirectly for the unknown so-called root factors. In 1957, Person, Samborski, and Forsyth (10) demonstrated that both chlorophyll degradation and protein loss in detached wheat leaves are retarded if the blades are floated on solutions of benzimidazole at 50 mg/liter. In the same year, Richmond and Lang (12) showed that similar effects could be obtained if excised leaves of Xanthium are kept with their petioles dipping into solutions of kinetin at 5 mg/liter. Mothes and Engelbrecht (5) sprayed solutions of kinetin directly onto leaves of Nicotiana and reported (1959) that the retention of chlorophyll is localized to the areas of the blade to which kinetin is supplied. They found that labelled amino acids migrate to, and accumulate in, the treated parts of tobacco leaves, and they suggest that kinetin retards leaf senescence by causing the treated areas to act as loci for the accumulation of metabolites (5, 6). Extensive investigations have shown that both protein synthesis and ribonucleic acid synthesis is stimulated in kinetin-treated parts of tobacco leaves. (15). Mothes and Engelbrecht (7) conclude, however, that "accumulation, . . . is not the consequence of synthesis, but mass synthesis of protein, for example, is the consequence of an accumulation of amino acids." In 1959, (8) it was demonstrated that a number of auxins are markedly effective in retarding the senescence of attached or detached autumn leaves of Prunus serrulata-senriko. Where ethanolic solutions of esters of 2,4-dichlorophenoxyacetic acid are applied to the blades, the cells retain their green color for some 10 to 20 days longer than those in the surrounding untreated parts of the blade, or in the control leaves. The retention of green color in the treated areas is associated with an actively photosynthetic chlorophyll and, a maintenance of the initial protein level (9). Attempts to retard senescence by various treatments with kinetin proved unsuccessful in this species. Precise information is still meagre concerning the part played by either auxins or kinins in the retardation of the biochemical changes associated with senescence but it is clear that they must exert a control through some fundamental cellular processes. In this paper are described some effects of one kinin, kinetin, upon the metabolism of protein and nucleic acids during the senescence of excised leaves of Xanthium pennsylvanicum. The results provide evidence that kinetin may control senescence in these 1 Received Jan. 15, 1962. 2 Present address: Agricultural Research Council Unit of Experimental Agronomy, Department of Agriculture, Oxford.
304 citations
238 citations
TL;DR: Im Entwicklungsablauf der h6heren Pflanze stehen Organverluste (Laubfall) oder Absterbevorg~tnge bestimmter Gewebe (Borke, Kernholz) in charakteristischem Wechsel mit Restitutionen, damit totipotenten, teilungsf~ihigen Bezirken (Meristemen) nehmen.
209 citations