Tree Dev Midterm

central cylinder meristem

contributes to the outer vascular tissues

cortex mother cells

part of the main dividing cells, contribute to the formation of the root meristem

central mother cells

part of the main dividing cells and production, contribute to the formation of the meristem, root cells, and vascular tissues and innermost tissue

columella mother cells

dividing cells located near the root tip that lead to the development of the columella system and outer cells and formation of the root cap, extends the root

columella

contains specialised cells that sense gravity

root cap

acts as a protector to the root internal parts and produces mucilage to help push through soil

differentiation

The process where newly generated cells from the root apical meristem specialize in structure and function and form mature primary and secondary tissues of the root system. Differentiation involves cells dividing, elongating and expanding. The zone of differentiation is in the root tip.

factors that impact root growth

root initiation (lateral or adventitious), root growth (elongation), root growth periodicity (seasonal and episodic) and dormancy, internal and external control, root growth potential

root initiation: lateral - 1st root growth factor

formed by following a pattern related to the pattern of primary xylem and phloem. factors including sugars, vitamins and plant growth regulators leak radially from vascular tissues to feed development of new lateral roots. can be inhibited with abscisic acid - ABA - which is a plant growth regulator that acts as an inhibitor. ABA forms at the root tips in response to stress, esp water stress

root initiation: adventitious - 1st root growth factor

form after wounding occurs to the main roots - root pruning or undercutting. begins by a callus tissue forming over the wound from surrounding parenchyma cells followed by lateral meristemoids forming within the callus

auxins

main plant growth regulator

root growth - elongation - 2nd root growth factor

auxins at low concentrations promote root growth. stress increases ABA production which decreases or inhibits root growth. carbs from crown activity promotes root growth. restricted light or liquid inhibits root growth. factors impacting shoot growth also impacts root growth.

root growth periodicity - seasonal and episodic - 3rd root growth factor

1st peak: spring, associated with bud growth and soil moisture. 2nd peak: autumn, associated with export of carbs from crown to root system

individual root growth cycle

independent of each other, elongation 2-3 weeks, acropetal browning, browning of apex, necrosis of outer cells, dormancy, swelling and emergence of new white apices through brown layer

elongating root - white root

white, no root hairs, 10cm elongation in one growth cycle, root diameter proportional to elongation, root cap

absorbing root - white root

initiate root hairs, 3 cm elongation, root cap

brown roots

enveloped by necrotic layer, root cap reduced and rounded, occurs between periods of elongation

dormancy

cessation of elongation occurs and the stele and secondary endodermis differentiate to within a few cells of the central zone

external control factors - 4th root growth factor

temperature, aeration, moisture, mineral availability, soil composition, competition

internal control factors - 4th root growth factor

photoperiod, shading (light intensity), air temperature, defoliation, flowering and fruit set, branch elongation, vigor and crown size, root shoot radio, thermoperiod

root growth potential - 5th root growth factor

the ability of a seedling to initiate and elongate roots when placed in an environment favorable for root growth. can predict field performance with physiological test of seedling quality when planting site conditions are similar