ZESZYT Nr  13/ 2013    Abstrakty
      Volume No. 13/2013     Abstracts


2. Inhibition of seed germination by far red radiation transmitted through leaf canopies- Tadeusz Górski, Krystyna Górska, Henryk Stasiak

Perception of light by phytochrome is one of the mechanisms that enable seeds to optimize the place and time of germination. In an effort to determine how widespread in nature is the
inhibition of seed germination by light transmitted by competing plants, the seeds of various species were exposed for germination beneath leaf canopies. A high ratio of far red (FR) to red (R) light under the canopies inhibited to various extent the germination in most of samples. Only 91 species (out of 487 tested) did not indicate any FR-inhibition and might be determined as truly light-insensitive. Although particular seed samples of the same species often differ in response to white light (photoblastism), the responses to the FR irradiation seem to be much more stable. The ability to the FR-dormancy may be treated as a species-specific feature. After several-day exposure under leaf canopy, the seeds become extremely sensitive to the white light, but this sensitivity diminishes slowly in the course of treatment. Every seed cohort may be diversifi ed in germination by the irregular and variable
structure of leaf canopy. The acquired state of photosensitivity may persist during several years and may impact on seed longevity.
The seeds needing winter prechilling (stratifi cation) for a substantial germination, often become more indifferent to the white light, but always show a FR-sensitivity. The relations between taxonomic position and FR-sensitivity are weak. No difference in the FR-sensitivity was observed among life-forms. Distinct relations were stated between seed size and FR-sensitivity; seeds of FR-insensitive species are in average much larger. A relationship
was found between the dynamics of germination and the photoresponses.
Positively photoblastic and FR-sensitive seeds usually need much more time to full germination. These relationships may explain the fact that often the seeds of cultivated plants are photoblastically indifferent and FR-insensitive; they have been selected for fast and uniform germination. Full daylight exerted usually an inhibitory effect on germination of seeds of almost all tested species. The concept of positive photoblastism ought be treated with caution, because it proves true only in weak light.

far red irradiation, leaf canopy, seed germination, seed longevity, seed photosensitivity