Question

Venning (1949) and Walker (1957) studied the effect of wind on celery collenchyma and found that while the number of collenchyma bundles remained unchanged, larger areas of heavier collenchyma with heavier cell wall thickenings developed at an early stage of the experiment. Walker (1960) measured the length of the collenchyma cells in Datura stramonium and found that mechanical stimulation decreased their size and thus inhibited elongation. Critically evaluate the experiments results of both plants.

Answer 1

Ans: In modern study affect of wind on plant growth is termed as thigmomorphogenesis or seismomorphogenesis and plants undergoes adaptive response for the condition by changing their tissues mechanical properties or mechanically induced stress (MIS) by thinning or thickening.

Venning (1949) compared celery plant petioles exposed to constant wind and windless environments. He observed that even though same number of collenchyma bundles are present in both the plants, plants exposed to wind motion stimulated the development of collenchyma within the bundles, resulting in larger areas of collenchyma, heavier thickenings of the cell wall, and collenchyma cells of larger diameter. That means collenchyma occupied more space and because of cell wall elongation and wall thickening and not by increasing the number of collenchyma bundle cells. He opined that to tolerate and survive mechanical stress more cell wall materials are deposited (cellulose, hemicellulose and lignins). For elongation he did’t provide a satisfactory explanation, however later research found that once the wall thickening starts in collenchyma bundles they start elongating, this will be higher in plants with mechanical stress. One they are thick, elongated and matures they have a property of high tensile strenth and plasticity.

Walker (1957) observed that Cell wall thickening increased but collenchyma cell elongation decreased in Datura stramonium. plants which were subjected to mechanical shaking for 9 hrs daily for 40 days produced more heavily thickened collenchyma cell walls compared with control plants, but mechanical induced stress inhibited collenchyma cell elongation. The explanation can be, he subjected to mechanical shaking for 9 hours where as venning did it with wing continuously. Thickening of call wall and elongation might have provided mechanical strength in case of venning, but in the case of Walker wall thickening is enough to withstand stress for 9 hours. However it may differ from plant to plant for example in plants with secondary growth (for datura it is possible compared to celery) xylem, phloem and pith takes care of mechanical stress and parenchyma tissue does not involve in taking mechanical stress, parenchymal bundle elongation may not be required.