عنوان

Morphogenetic analysis of apical branching in a temperature-sensitive mutant of Aspergillus niger. An integrated study of physiology, cytology, and computer simulation of growth

TLpq304285559

انگلیسی

Morphogenetic analysis of apical branching in a temperature-sensitive mutant of Aspergillus niger. An integrated study of physiology, cytology, and computer simulation of growth

[Thesis]

C. G. Reynaga-Pena

S. Bartnicki-Garcia

University of California, Riverside

1996

100

Ph.D.

University of California, Riverside

1996

To study the mechanisms involved in apical growth and morphogenesis in fungal hyphae, we isolated a temperature-sensitive mutant of Aspergillus niger (ramosa-1) capable of apical branching after a shift from 23C to 34C. Video-enhanced phase contrast microscopy allowed us to observe, record and analyze the events leading to apical branching. First, a localized momentary contraction lasting about one second caused the sudden unidirectional movement of visible organelles towards the hyphal apex. During the contraction, a transitory sharp increase in refractive index occurred in a localized area of cytoplasm. During the next 10 s, the Spitzenkorper retracted from its polar position at the apical pole and eventually disappeared. During this period the rate of hyphal elongation was sharply reduced, and organelles clustered 5-10 mum behind the tip. After a period of relatively little growth, polarized extension resumed with the appearance of two new Spitzenkorper, each giving rise to a branch at the apex. Cytoplasmic contractions affected the stability of the Spitzenkorper. The morphogenetic process of apical branching in ramosa-1 was duplicated with the Fungus Simulator program. Simulation of this complex sequence gave us a unique opportunity to test the mathematical hyphoid model of fungal growth and morphogenesis. We simulated the entire apical branching process by programming the movement and vesicle release rate of the VSC in the model to follow the Spitzenkorper position and corresponding rate of area increase. The predictive power of the model was used to determine which pattern of vesicle discharge operates when a Spitzenkorper is not detectable. The onset of polarized growth prior to branch development was modeled by programming multiple VSCs in the vicinity where growth occurred. Our results support the idea that the Spitzenkorper acts as a VSC, and is therefore directly responsible for the morphogenetic events during apical branching. Analysis of pulsed growth in the wild type and the mutant showed that hyphae from both strains had pulses of similar frequency (7-11 pulses per min) despite substantial differences in elongation rate. The ramosa-1 mutant allowed us to analyze growth pulses in adjoining branches arising from the same parent hypha. Pulses in these closely connected hyphal branches were of similar frequency but were not synchronous. We concluded that the final events in the discharge of wall-building vesicles responsible for apical growth are controlled locally at each growing point.

"orper

Biological sciences

Cellular biology

Genetics

Microbiology

Spitzenk

C. G. Reynaga-Pena

S. Bartnicki-Garcia

p

[Thesis]

276903

a

Y