Studies on the effects of temperature on the growth of plant tissue culture

Abstract

#1. Tissue explants from Jerusalem artichoke (Helianthus tuberosus L.) have been used in this study. It has been shown that these explants can be grown successfully on a nutrient agar medium containing inorganic salts, sucrose, coconut milk and 2:4-D. The presence of coconut milk and 2:4-D ensures rapid and sustained growth.

#2. A detailed analysis of the growth of explants at several different temperatures has been made. Changes in fresh weight, dry weight, cell and tracheid number, volume and anatomical structure have been studied at 10°, 12.5°, 25°, 30°, 32.5°, 35°, 37° and 40°C.

#3. Approximate determinations of the maximum, minimum and the optimum temperatures for growth have been made.

#4. The growth pattern of the explants falls into two distinct phases, one of dedifferentiation and a subsequent one of differention. The first phase may be further subdivided into two periods, a lag period and a subsequent period of growth in which the cell number of the explant increased exponentially. A third period of growth, the final or post-exponential period extends into the differentiation phase.

#5. Temperature affects the two phases and the periods of growth as well as their component processes of cell expansion and cell division.

#6. Temperature also affects the differentiation of tracheids and meristematic nodules in the explant.

#7. The lag period for fresh weight increase was markedly affected by temperature. The lag period was longest at 10°C and decreased in length with the rise in temperature up to 37°C. At 40°C no increase in fresh weight could be detected.

#8. The lag period for the increase in cell number was also markedly affected by temperature. The lag period was longest at 10°C and its length decreased with a rise of temperature up to 35°C. No increase in cell number was detected in explants grown at 37°C or above.

#9. It appeared that the first cell division in the explants cultured at 25°C, occurred in a 'wave' or semi synchronously.

#10. An attempt has been made to study the effect of temperature on some stages of cell division cycle. The pre-DNA synthesis period (G₁) was found to be less temperature sensitive than the combined period of DNA synthesis (S), post DNA synthesis period (G₂) and mitosis (M), (S + G₂ + M).

#11. The techniques of autoradiography and cytophotometry of Feulgen-stained nuclei were used to study the changes in the DNA content of the nuclei. It has been shown that almost all of the constituent nuclei of the explant are 2C at excision and that their DNA content increases to 4C prior to cell division.

#12. It has been observed that lowering the temperature slows. down the process of replication of DNA from 2C to 4C.