Influence of Root Zone Calcium on Maintenance of Potato Shoot Tip

Abstract

Calcium deficiency in the potato shoot results in sub-apical necrosis. This is a physiological condition whereby necrotic lesions form a few millimeters below the shoot apex ultimately causing shoot tip senescence, loss of apical dominance, and the release of axillary buds. Using a Dark Red Norland tissue culture system, we studied the relationship of root zone calcium levels to shoot tip maintenance. Root zone calcium levels lower than 50 ppm resulted in shoot tip death and prolific branching from axillary buds. Chelator studies with EGTA and tracer studies with 45 Ca, indicated a direct involvement of calcium at the shoot tip for shoot tip maintenance. Interestingly, low root zone calcium deficiency syptoms could be mitigated with 0.001 to 0.01 μM of the auxin analog NAA. Developmental studies of calcium deficiency symptoms indicate no anatomical relationship with shoot tip necrosis as xylem conducting elements were found near the shoot apex regardless of the root zone calcium level. These results have important implications for potato shoot development especially during the early development stage from the seed piece.