Question

Why do small seeds commonly need “high quality” light exposure to germinate? What does “high quality” light mean from a plants perspective??

Answer 1

• Seed germination is dependent on light.As well various seeds require varied degrees of sunlight.some seeds require maximum temperatures ,some germinate at minium temperature while some require optimal ranges.
• Light acts as a signal to initiate and regulate photoperiodism and photomorphogenesis. There are two light-sensing systems involved in these responses, the blue light sensistive system and the red light sensitive or phytochrome system.
• Seeds of certain plants require red light for germination; FR light inhibits germination. Many small seeds with low amounts of storage reserves (such as lettuce) show such a red light requirement.
• If these seeds they are buried below the level of light penetration in the soil, they do not germinate.
• If they are shaded by a leaf canopy, causing a high proportion of FR, germination is inhibited, Pfr is required for germination.
• Tiny seeds are sown and left uncovered so that they get abundunt light exposure which is needed for their germination.
• The light requirement of a seed depends on the habitat it grows.For example a seed requiring light to germinate might fall into the deep shade of another plant where growing conditions would be very poor, whereas a seed falling into an open, well lit space would germinate quickly and flourish.
• On the other hand, it may be essential for the establishment of the young seedling that part or all the seed needs to be covered with soil or in the shade, perhaps, to protect the young root.
• In such a case with a seed which required darkness, uncovered seed, which is exposed to light will not germinate.
• Sometimes only part of the seed is light sensitive. Phacelia is light sensitive at only two points on its surface and in a lettuce at only one. The micropyle where the water is absorbed, is light sensitive perhaps to ensure that only correctly oriented seed with the best chance of survival germinates.