Photoinhibition of Seed Germination in Mediterranean Maritime Plants

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Abstract
Photoinhibition of seed germination was shown for Allium staticiforme, Brassica tournefortii, Cakile maritima and Otanthus maritimus, all plant species inhabiting sandy coasts of the Mediterranean Sea. Germination of A. staticiforme was found to be typically Mediterranean in regard to its temperature range (>0–20 °C), while B. tournefortii germinated optimally at intermediate temperatures (15–25 °C). Light sensitivity was more pronounced in the latter species and 50 % inhibition of seed germination was obtained with photon flux densities of approximately 0.1 and 0.015 mol m−2 d−1 in A. staticiforme and B. tournefortii, respectively. However, the slopes of the regression lines of germination plotted against the logarithm of white light flux density are similar in both species. From monthly experiments performed under fluctuating conditions of temperature and light, simulating the elimate of Athens throughout the year, optimal germination response peaked in ‘winter’ conditions for A. staticiforme, while a bimodal pattern was observed for B. tournefortii (maxima at the warm ends of the rainy season). In contrast to the other plants, a fifth species tested, Crithmum maritimum, showed an absolute light requirement, probably related to the rocky habitats of the species; the optimum germination period coincided with the rainy season. Pot experiments with seeds of the five species buried at various depths confirmed that maximum emergence is favoured by shallow depths (0.5–1 cm). It is concluded that seed germination in maritime plants of the Mediterranean rim is mediated by a photoinhibition mechanism which can be considered an adaptation strategy against surface seedling establishment at the harsh, sandy or shingle, sea coast habitats.

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