Date of Award
Doctor of Philosophy in Biological Sciences
Luke S. Albert
Physiological factors and conditions accompanying anthocyanin synthesis and morphogenesis in the hypocotyl of Impatiens balsamina L. were investigated with the objective of showing relationships between a biochemical process (anthocyanin synthesis) and morphogenetic events (the formation of epidermal hairs and roots, elongation of the hypocotyl, straightening of the hypocotyl arch), which may yield information on the physiological control of growth and development. The scope of the problem includes a study (1) of the hypocotyl anatomy, (2) of the effects of chemical agents on the development of anthocyanins, roots, and epidermal hairs in cultured hypocotyl segments and (3) of the photocontrol of anthocyanin synthesis, hypocotyl elongation, and the straightening of the hypocotyl arch by specific regions of the visible spectrum.
Hypocotyl anatomy was studied by preparing sections from preserved 5 and 10-day-old etiolated seedlings by the paraffin technique and hand sections of fresh tissue from 15-day-old light grown seedlings. Free-hand drawings were made of the paraffin sections. A gradient of differentiation from meristematic at the cotyledon end (the pseudomeristem) to mature primary tissues at the base of the hypocotyl is described. The elongation of the hypocotyl arose from cell division in the pseudomeristem and cell elongation in the region just below the hypocotyl arch. The hypocotyl arch is formed through differentiated hypodermal cell layer.
An axial gradient of respiration for the hypocotyl was determined by measuring the rates of oxygen consumption of segments of the hypocotyl in a Warburg respirometer. The maximum rates of respiration occurred in the region of the pseudomeristem when expressed on a fresh weight basis and in the region of cell elongation on a per cell basis.
To study the effects of chemical agents, 7-day-old etiolated hypocotyls grown under sterile conditions were cut into 10 segments and cultured on an agar medium supplemented with the following chemicals either singly or in combinations: (1) sugars - sucrose and glucose, (2) growth substances - Naphthalene acetic acid (NAA), Triiodobenzoic acid (TIBA) and Gibberellic acid (GA.)., (3) compounds known to effect anthocyanin synthesis - Azaguanine (Aza), Benzimidazole (Bz) and Riboflavin (Rb) . Periodic observations on growth (root and hair formation) and anthocyanin synthesis in the hypocotyl segments were made over a period of 10 days. Glucose supported better anthocyanin synthesis than sucrose, while sucrose supported better growth of the hypocotyl segments. Results from experiments using the growth substances and the purine analogues (Aza and Bz) indicate that growth and anthocyanin synthesis are closely integrated and that their coordination is dependent on an unaltered purine metabolism. Evidence is presented that endogenous auxin levels can simultaneously influence root and hair formation, and the quantitative distribution of anthocyanins along the axis of the hypocotyl. Rb inhibited anthocyanin synthesis generally and inhibited root and hair formation in segment l.
The high energy action spectra for anthocyanin synthesis, inhibition of hypocotyl elongation, and straightening of the hypocotyl arch were determined using monochromatic light sources. All three responses of the hypocotyl were shown to be photoreversibly controlled by the low energy phytochrome reaction through the use of filtered fluorescent and incandescent light. Action maxima for the high energy reaction were found at 425 mu for anthocyanin synthesis and hypocotyl elongation and at 441 mu for the straightening of the hypocotyl arch. The similarity of the action spectra indicate that a single photoreceptor was active in all three responses. It is suggested that the high energy photoreceptor is phytochrome itself and a model photomorphogenic system is proposed.
Arnold, Allan Windsor, "Factors Affecting Anthocyanin Synthesis and Morphogenesis in the Hypocotyl of Impatiens Balsamina L." (1962). Open Access Dissertations. Paper 795.