Diurnal variations of hydrocyanic acid, dry matter, and total sugar in sorghum strains

A study was conducted on the diurnal changes in hydrocyanic acid, dry matter, and total sugar content in five strains of Dakota Amber selected on the basis of their hydrocyanic acid content. Two strains were tested in 1939 and five strains in 1940. Diurnal variation of hydrocyanic acid in different sorghum strains showed unlike trends during the daytime, although in every case the greatest diurnal drop in hydrocyanic acid content occurred at the close of the day between 6:00 and 8:00 p.m., when photosynthetic activity was low. Similarly, the most rapid diurnal increase in hydrocyanic acid occurred between 8:00 and 10:00 p.m., when reduction in dry matter and total sugars of the leaves had taken place. Hydrocyanic values from sorghum strains sampled at different diurnal periods suggest that unless samples of strains to be compared are taken simultaneously, it may be difficult to get a correct evaluation of the material under study. The diurnal maximum hydrocyanic acid content in the five sorghum strains tested occurred at different quarterly periods. Their diurnal minimums also occurred at different quarterly periods. Similar diurnal hydrocyanic acid trends were found in sorghum strains sampled on a warm, bright, clear day or on a cool cloudy day. Diurnal variations in the trend of hydrocyanic acid content in a sorghum strain sampled at a similar stage of growth in different seasons were similar. The greatest variation for strains between seasons was their mean hydrocyanic acid content. Environment and stage of growth of sorghum plants apparently affected their hydrocyanic content. Dry matter in the leaves of sorghum strains tested began to increase after 4:00 a.m. The diurnal maximum dry matter content occurred between 2:00 and 6:00 p.m. Minimum dry matter content in the sorghum strains occurred about 4:00 a.m. Hydrocyanic acid content in sorghum strains evidently is associated with photosynthesis, being at a maximum during the daytime, shortly after the dry matter in the sorghum leaves was at its maximum. The diurnal variation in the concentration of hydrocyanic acid in sorghum strains is apparently positively correlated with the diurnal variation of total sugar in the leaves. Generally, the hydrocyanic acid change came about later than the change in sugar content. The higher the rate of change in the sugar content, the more rapid was the change in hydrocyanic acid content. Variability in hydrocyanic acid content is also associated with other photosynthetic activities. Diurnal variation of hydrocyanic acid content in sorghum is the function of three variables, as follows: (A) The genetic constitution of strains; strains have been isolated which do have definite hydrocyanic acid levels and diurnal trends. (B) Environmental factors; the growth and development of the sorghum plant influences the hydrocyanic acid content. A higher or lower hydrocyanic acid content level caused by environmental factors did not appear to affect the diurnal hydrocyanic acid trend in a sorghum strain. (C) Photosynthetic activities; assimilation of photosynthetic products causes unlike variations in the diurnal hydrocyanic acid trend within sorghum strains at short intervals of time.