, Volume 7, Issue 3, pp 133-144

Hormones andCuscuta development: In vitro induction of haustoria by cytokinin and its inhibition by other hormones

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Abstract

Cytokinins induced haustoria formation in excised 10-mm segments ofCuscuta vine, the subapical 25-to-50-mm region being most responsive, producing a mean of 4–6 haustoria per segment. The order of effectiveness of cytokinins continuously applied (72 h) was 6-benzylaminopurine (BA) ⩾ isopentenyladenine (iP) ≫ zeatin (Z). Ribosides of BA and Z were as effective as the bases, whereas riboside of iP ([9R]iP) was half as effective as iP. Haustoria induction was influenced by weather and seasonal conditions at the time of vine collection; materials obtained on warm, sunny days responded better than those obtained on rainy, cloudy, or cool days. Haustoria were induced equally well all around the segment, and no thigmostimulus was needed for induction. p ]A 10-min pulse of 100 μM BA induced half as many haustoria as a 60-min pulse or continuous application of BA. White light inhibited haustoria induction elicited by a short (30-min) pulse of BA, whereas a longer (120-min) BA application overcame this light inhibition. Auxins (IAA or NAA, 1–10 μM), gibberellin (GA3, 1–10 μM), ethylene (as ethrel, 10–100 μM), and abscisic acid (ABA, 100 μM) were individually inhibitory (60–80%) with respect to haustoria induction when given continuously with 50 μM BA. A 60-min pulse of auxins (10 μM), GA3 (100 μM), or ethrel (10 μM), given at various time intervals during or after a 60-min pulse of 100 μM BA, showed that inhibition was maximal (70–95%) between 4 and 16 h of BA application and negligible (GA3) or much reduced (auxin, ethrel) at 20 h, indicating a “commitment” to haustoria formation by this time.