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PubMed2005

Maintenance of embryonic auxin distribution for apical-basal patterning by PIN-FORMED-dependent auxin transport in Arabidopsis.

Molecular mechanisms of pattern formation in the plant embryo are not well understood. Recent molecular and cellular studies, in conjunction with earlier microsurgical, physiological, and genetic work, are now starting to define the outlines of a model where gradients of the signaling molecule auxin play a central role in embryo patterning. It is relatively clear how these gradients are established and interpreted, but how they are maintained is still unresolved. Here, we have studied the contributions of auxin biosynthesis, conjugation, and transport pathways to the maintenance of embryonic auxin gradients. Auxin homeostasis in the embryo was manipulated by region-specific conditional expression of indoleacetic acid-tryptophan monooxygenase or indoleacetic acid-lysine synthetase, bacterial enzymes for auxin biosynthesis or conjugation. Neither manipulation of auxin biosynthesis nor of auxin conjugation interfered with auxin gradients and patterning in the embryo. This result suggests a compensatory mechanism for buffering auxin gradients in the embryo. Chemical and genetic inhibition revealed that auxin transport activity, in particular that of the PIN-FORMED1 (PIN1) and PIN4 proteins, is a major factor in the maintenance of these gradients.

Arabidopsis↗
PubMed1978

Gradient of Growth, Spontaneous Changes in Growth Rate and Response to Auxin of Excised Hypocotyl Segments of Phaseolus aureus.

Spontaneous growth was studied in excised mung bean (Phaseolus aureus Roxb.) hypocotyl segments. Measurements were made with a growth-recording apparatus using displacement transducers on single 5- to 6-millimeter samples excised from the growth zone immediately below the hook.Even for a given zone and under controlled experimental conditions, there are differences in the spontaneous growth of individual explants. Nevertheless, in every case, two phases of endogenous acceleration are found at 15 to 20 minutes, and 120 to 150 minutes after excision. Accelerations were separated by steady growth phases. Knowledge of the spontaneous growth curve appears important for the choice of the time of application of experimental stimuli. Auxin was added at various times after excision (0 to 6 hours). The classical biphasic response to auxin was obtained when the hormone was added during a steady phase of growth. However, the response was difficult to interpret when the hormone was added during an acceleration phase.Spontaneous and indoleacetic acid-induced growth were studied along the hypocotyl. Spontaneous growth rate and growth potential revealed by indoleacetic acid changed markedly along the growth gradient. The nature of spontaneous changes according to experimental time and state of differentiation of the cells is discussed.

Journal Article↗