Interaction with gravitropism, reversibility and lateral movements of phototropically stimulated potato shoots.

D Vinterhalter,M Stanišić,J Savić,B Vinterhalter,Ž Jovanović

doi:10.1007/s10265-016-0821-4

Abstract

Phototropic (PT) and gravitropic (GT) bending are the two major tropic movements that determine the spatial position of potato shoots. We studied PT bending of potato plantlets grown under long-day photoperiods in several prearranged position setups providing different interactions with the GT response. Starting with the standard PT stimulation setup composed of unilateral irradiation of vertically positioned shoots, experiments were also done in antagonistic and synergistic setups and in treatments with horizontal displacement of the light source. In the standard setup, PT bending suppressed the GT bending, which could occur only if the PT stimulation was cancelled. The antagonistic position, with phototropism and gravitropism attempting to bend shoots in opposite directions, showed phototropism and gravitropism as independent bending events with the outcome varying throughout the day reflecting diurnal changes in the competence of individual tropic components. Whilst gravitropism was constant, phototropism had a marked daily fluctuation of its magnitude with a prominent morning maximum starting an hour after the dawn in the growth room and lasting for the next 6 h. When phototropism and gravitropism were aligned in a synergistic position, stimulating shoot bending in the same direction, there was little quantitative addition of their individual effects. The long period of morning PT bending maximum enabled multiple PT bending events to be conducted in succession, each one preceded by a separate lag phase. Studies of secondary PT events showed that potato plantlets can follow and adjust their shoot position in response to both vertical and horizontal movements of a light source. PT bending was reversible, since the 180° horizontal change of a blue light (BL) source position resulted in reversal of bending direction after a 20-min-long lag phase.Electronic supplementary materialThe online version of this article (doi:10.1007/s10265-016-0821-4) contains supplementary material, which is available to authorized users.

Highlights

Potato plantlets propagated in vitro by single node explant subculturing have been recently employed to study tropic responses of dicotyledonous plants (Vinterhalter et al 2012, 2015)
Positioned light from a blue light (BL) source mimics early morning light in nature, and GT stimulation is absent until shoot tips start to bend toward the BL source
PT and GT interactions have been studied in a number of light-grown or de-etiolated plant species, including sunflower (Franssen 1980), cress (Hart and Macdonald 1981) and Arabidopsis (Fukaki et al 1996a, b)

Summary

Introduction

Potato plantlets propagated in vitro by single node explant subculturing have been recently employed to study tropic responses of dicotyledonous plants (Vinterhalter et al 2012, 2015). Grown under long-day (16 h light/8 h dark) conditions, these plantlets performed vigorous PT and GT bending movements. PT and GT bending magnitudes were subjected to regular daily changes in accordance with a specific diurnal rhythm. An hour after the lights in the growth chamber were turned on (dawn at 7.00 h), the PT response reached its daily maximum, which lasted through the 6–7 h, declining in the afternoon and staying low during the night. Diurnal changes of the GT response magnitude were less prominent, but they alternated with the PT response changes with highest values at dawn, late in the afternoon and during the night. Detection of diurnal changes in the magnitude of PT and GT responses forced us to abandon the classic view of the PT response as a constant and predictable feature of etiolated or de-etiolated seedlings.

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Conclusion