Germination Of Light-sensitive Seeds Research Articles

Assessing the impact of porosity variations on the reflectance and transmittance of natural sands

Porosity is a fundamental characteristic of naturally occurring sand-textured soils, commonly referred to as natural sands, found in a wide range of landscapes, from beaches to dune fields. As a primary determinant of the density and permeability of sediments, it represents a pivotal element in geophysical studies involving basin modeling and the optical dating of sand deposits formed in areas subjected to erosion like coasts and deltas. It is also of interest for geoaccoustics and geochemical research on sediment transport and water diffusion properties of these deposits, as well as for agricultural and ecological investigations on the germination of light-sensitive seeds and the photochemical transformation of substances (e.g., pesticides) that may be present in these soils. Despite the importance of these applications, however, the remote estimation of porosity and the quantification of its effects on the light penetration profiles of natural sands remain elusive tasks. In this work, we tackle one of the major obstacles in this interdisciplinary area of research, namely the relative scarcity of experimental information due to technical constraints associated with traditional laboratory procedures. More specifically, we systematically examine the impact of porosity variations on the reflectance and transmittance of natural sands (in the 400 to 1000 nm region of the light spectrum) through controlled in silico experiments supported by measured data. Our findings are expected to strengthen the knowledge basis required for advances in this area and contribute to the development of technologies aimed at the effective monitoring and prediction of environmentally triggered changes affecting these soils.

Similar Effects of Blue and Infra-Red Radiation on Light-sensitive Seeds

EVIDENCE that blue spectral regions affect the germination of light-sensitive seeds has existed for some years, and has recently been confirmed for both light-inhibited1 and light-promoted seeds2,3. Borthwick et al. 2 obtained both promotion and inhibition of germination of lettuce seed by blue radiation, depending on the duration of the period the seeds had been allowed to imbibe water prior to irradiation. Evenari et al. 3 have also reported both stimulation and inhibition by blue light, depending on the imbibition period. It is well known that infra-red is also inhibitory to the germination of lettuce seed and that there is a specific interaction between infra-red and red radiation, the effects of red being reversible by infra-red and vice versa. A similar specific interaction between red and blue light has apparently not previously been reported, although Flint and McAlister4 showed that a long exposure of lettuce seed to blue spectral regions nullifies the promoting effect of a previous exposure to red. In the following experiments it was shown that the action of blue is effectively similar to that of infra-red.

Photoreversibility of Leaf and Hypocotyl Elongation of Dark Grown Red Kidney Bean Seedlings

Many of the light-controlled responses of plants are known to be most effectively regulated by radiation in the red region of the spectrum. Among these are such diverse phenomena as initiation of flowers in photoperiodically sensitive plants (7), germination of light-sensitive seeds (3), pigmentation of the tomato fruit cuticle (9), and growth of parts of dark-grown seedlings (1, 5, 6, 8). In 1952 Borthwick et al (3) found that far-red radiation near 7350 A given after a treatment with red reversed the promotive action of the red on germination of light-sensitive lettuce seeds and thus left the seeds in a non-germinating condition. Far-red was also found to reverse the action of red in the control of flower initiation in short-day plants (2, 5) and pigmentation of the tomato fruit cuticle (9). More recently Liverman et al (6) showed that the red reaction inducing expansion of bean leaf discs was reversed by far-red, and Withrow (11) demonstrated the far-red reversal of the red reaction that leads to the straightening of the plumular hook of excised bean hypocotyls. The photoreaction has been shown to be repeatedly reversible. A succession of alternate red and farred irradiations on light-sensitive seeds (3, 4) showed that germination depended upon the quality of the energy last received. That is, when the seeds received red energy last, they germinated, but when they received far-red energy last, they did not germinate. The red action for the control of pigmentation of the tomato fruit cuticle (9), flower initiation of cocklebur (5), and straightening of the plumular hook of excised bean hypocotyls (11) has also been shown to be repeatedly reversible by far-red. Such results indicate that the actions of red and of far-red are the reversal of a single reaction. The purpose here is to demonstrate the existence of the same photoreversible reaction in controlling elongation of leaves and hypocotyl of intact darkgrown seedlings of Red Kidney beans and to investigate some of the details of the response.

NOTE ON PHOTOSYNTHETIC ACTIVITY IN SEEDS OF THE SPIDER LILY

THE IDEA of a foliar origin of the ovule is of long standing in botany, and perhaps as a corollary it may be noted that there are many evidences of the persistence of chlorophyllous tissue in seeds. For the most part this persistence appears juvenile within translucent ovaries, disappearing with the development of opacity in the enveloping structures; yet it may be assumed that the elaborated carbohydrates contributed to the development of seed structures. Flint (1938) indicated that the quality of light absorbed by the chlorophyllous tissues of maturing seeds and the enclosing carpels appeared related to the property of light-sensitivity in seeds. Such phenomena as the greening of seedlings in light and the relation of quality of light to the germination of light-sensitive seeds as reported by Flint and McAlister (1937) involve chlorophyll in macroscopically non-green tissue, yet may be cited as further instances of the persistence of chlorophyll. Ordinarily the principal source of organic reserves making possible the development of the ovule in the higher plants is the chlorophyllous tissue of the parent plant. Compared with this source the photosynthetic activities of the embryo or of the accessory surrounding tissues are meager and transitory. In the seeds of the spider lily, however, and probably in seeds of a similar nature, there is normally a delayed growth of the very young embryo accompanied by a development of accessory tissues (Whitehead and Brown, 1940). There is no obvious concentration of organic reserves for the maintenance of the embryo and for its support during germination. Instead, such organic reserves as are supplied by the parent plant through the funiculus are utilized in the extensive elaboration of the accessory tissues. The integuments develop into a somewhat elaborate chlorophyllous tissue with sto1 Received for publication November 9, 1942. mates, underlain with parenchyma and vascular strands. Such a development carries with it the implication of functional activity for the chlorophyllous tissue, but the direct demonstration of photosynthetic activity is rendered obscure by the failure of the tissue to store starch and by the absence of dehydration and an attendant inactivity of a partially-developed embryo. Respiration may be assumed to be active in the developing embryo, contributing further to the utilization of carbohydrates. The developing embryos push through the seedcoats without the ordinary relation to soil and moisture, and even the formation of germling plants may take place on a laboratory table. It was found by Flint (1943), however, that immersion in water effected an abrupt arresting of the development of the embryo. Seeds thus immersed for ten months were found to have an unimpaired viability, however, resuming germination in the normal time and manner when removed from water. This discovery suggested the possibility of prolonging photosynthetic activity while embryo development was arrested and led to the experiments here reported. MATERIALS AND METHODS.-About ten quarts of seeds of the spider lily, Hymenocallis occidentalis, were collected on May 29, 1942. These were separated into groups on the basis of the weights of the individual seeds, as 4 to 5 gms., 5 to 6 gms., etc. The seeds selected were all green and firm, without injuries. Comparisons were designed to involve seeds of the same groups insofar as was possible. The selected lots of seeds were weighed, immersed in water for twenty-four hours, dried on moist paper towels, and re-weighed. They were then placed under the experimental conditions, which included immersion in series in water in large-bore pyrex glass tubes in the laboratory near a south window. Light was excluded from some of the tubes

Effect of Light on Germination of Light-Sensitive Seeds

1. The seeds of Rumex crispus, Datura Stramonium, and Phoradendron flavescens were found to be light sensitive. The germination of seeds of Rumex crispus and Phoradendron flavescens was promoted by light; the germination of seeds of Datura Stramonium was hindered by light. 2. Abrasion and removal of coats (ovary walls) of Rumex crispus seeds promoted their germination in darkness. 3. Treatment of seeds of Rumex crispus and Oenothera biennis with concentrated sulphuric acid caused an increase in the percentage of germination in darkness. 4. No reciprocal relation between the effects of light and temperature was found. 5. Light was not necessary for the absorption of sufficient water for germination. 6. Injection of water did not yield increased germination in darkness. 7. Almost all kinds of single electrolytes, regardless of the nature of the ions, seemed to promote germination of seeds of Oenothera biennis, Nicotiana Tabacum, and Verbascum Thapsus in darkness. 8. Embryos of seeds incubated in light becam...