Responding to the Environment Flashcards
skotomorphogenesis
Growth adapted to the dark, elongated hypoctoyl, closed apical hook, unextended cotyledons, no photosynthetic pigments.
Photomorphogenesis
Growth adapted to the light, arrested hypocotyl growth, opened apical hook, expanded and greened cotyledons.
why is skotomorphogenesis advantageous for the plant?
seeds are typically buried beneath the soil, with no access to light, hypocotyl elongation allows rapid growth through the soil to break the surface and reach light. this is often driven by dim light or negative gravitropism. closed apical hook protects the cotyledons as the hypocotyl pushes it through the soil.
how do seedlings bring about these responses to light?
seedling light responses are strongly related to auxin concentrations.in seedling shoots auxin strongly promotes cell elongation. In dark grown seedling the auxin concentration is high in the apical hook.
How do seedlings in light bring about responses?
PHYA and PHYB inhibit auxin synthesis and transport. PIF’s link changes to alter gene expression in PHYA/B to alter activity. This brings about auxin accumilation in the cotyledons causing expansion. Auxin in the hypocotyl dramatically decreases.
root development in nitrate deficiency
primary and lateral roots are elongated, no new roots are formed, this is because soil quality is heterogenous; longer roots are advantageous to reach deeper soil where nitrate may be accessible.
root development in the soil with abundant and heterogenous nutrient availability.
inhibition of primary root elongation, lateral root formation, strong increase in root density; due to the abundance of nutrients, the roots dont need to grow deeper. phosphate is very immobile in soil and is often abundant in the upper regions of the soil.
