Date of Award:

5-1969

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Botany

Committee Chair(s)

H. H. Wiebe

Committee

H. H. Wiebe

Committee

I. G. Palmblad

Committee

W. S. Boyle

Committee

R. L. Smith

Committee

C. Wayne Cook

Abstract

The effect of phenology on the pattern of photosynthate distribution was studied in crested wheatgrass (Agropyron cristatum (L.) Gaertn.) plants grown in a nursery under semi-natural environmental conditions. A set of plants was transferred every fourth week (April 13, 1968, through December 2, 1968) from the nursery to a growth room where the temperature was maintained at approximately 24 C with 16-hour photoperiods. A single leaf per plant received 1.5x10-3 ml of either NaH232PO4 or KH232PO4. Approximately 24 hours after the 32P application, the plants were harvested and dissected into various segments, oven-dried, and the amount of radioactivity in the different plant parts was determined with a thin window G-M tube and scaler.

The translocation of photosynthates in the early Spring prior to internode elongation was chiefly to the sheath of the tagged leaf. As the plants entered the boot stage, the amount of the upward and downward translocation of radiophosphorus was approximately equal. An increase in the amount of upward translocation from the tagged leaf was correlated with the early stages of flowering, followed by an increase in the amount of downward movement during the post-pollination stage. Shoot growth essentially ceased during the late summer when the plants were quiescent, but substantial 32P was transported to the underground portions of the plant. Analysis of the amount of total available carbohydrates indicated that they attained a maximum level in the roots and crowns during the period following sexual reproduction. Shoot growth was resumed in the fall after quiescence was broken,and the movement of 32P was initially to the roots followed by an increase in the amount of translocation to the tagged crown. At the time this stud y was terminated in December, the plants were covered with snow but a considerable amount of 32P continued to be translocated to the roots and crowns.

The effect of internal moisture stress and clipping on the pattern of photosynthate distribution was studied in crested wheatgrass and barley (Hordeum vulgare var. Hiland) plants grown in a controlled environmental growth chamber at approximately 70 percent relative humidity and 14-hour photoperiods. The ambient temperatures ranged from 15 to 21 C for crested wheatgrass and from 21 to 24 C for barley. Both species were subjected to two levels of defoliation and two levels of moisture stress. The plants grown under the high moisture stress regime were exposed to a one-cycle drought period in which the plants were not irrigated from 4 to 7 days previous to the application of radiophosphorus whereas the plants grown under the low moisture stress regime were irrigated daily. A single leaf per plant received 1.5x10-3 ml of the 32P solution, crested wheatgrass and barley, respectively. Approximately 24 hours after the 32P application, the plants were harvested and dissected into various segments, oven-dried, and the amount of radioactivity in the different plant parts was determined with a thin window G-M tube and scaler.

Defoliation, especially, in crested wheatgrass appeared to stimulate translocation from the basal portion of the tagged leaf blade. The primary effect of defoliation was to increase the amount of upward movement with less effect on the amount of downward translocation. The general effects of reduced moisture decreased the total amount of translocation from the tagged leaf. Reduced moisture increased the proportion of downward translocation of radiophosphorus.

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