Photocontrol of germination in Amaranthus caudatus |
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Authors: | Richard E Kendrick Barry Frankland |
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Institution: | (1) Queen Mary College, University of London, London, UK |
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Abstract: | Summary Germination of Amaranthus caudatus is inhibited by light, far-red being the most effective part of the spectrum. At temperatures of 25° and below there is a low final germination percentage under continuous far-red whereas above 25° there is only a delaying effect. In the presence of a saturating concentration of gibberellic acid (GA3) at 25° seeds germinate under continuous far-red although they are delayed. At 25° seeds exposed to 48 hr far-red fail to germinate when transferred to darkness. This induced dormancy can be broken by a single short exposure to red light given at any time after the far-red illumination. This effect of short red can be reversed by a subsequent short period of far-red indicating that the seeds are phytochrome controlled. Although most seeds have escaped from the reversing effect of short far-red after an intervening dark period of 5 hours, germination is greatly reduced by continuous far-red at this time. Results of exposing seeds to varying periods of far-red before and after dark imbibition are interpreted in terms of a continual production of phytochrome in its active P
fr
form and a requirement for P
fr
action over a long period of time. Effects of intermittent and continuous low intensity far-red on the inhibition of germination provides further evidence for a low energy photoreaction involving phytochrome. Effects on Germination Index of continuous illumination with various light sources maintaining different P
fr
/P
total
ratios have been investigated. The results suggest that the proportion of phytochrome in the P
fr
form is the most important factor in the regulation of germination. A scheme for the phytochrome control of germination in Amaranthus caudatus is presented and possible explanations for the dependence on P
fr
/P
total
ratio are discussed.Holder of a Science Research Council Studentship. |
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