No abstract

A coiling-inducing factor was isolated from tendrils of Bryonia dioica Jacq. and identified by infrared, (1)H-, (13)C-nuclear magnetic resonance and mass spectrometry as α-linolenic acid. When applied to detached tendrils, exogenous α-linolenic acid, but not linoleic acid or oleic acid, induced tendril coiling. Further investigations showed that metabolites of α-linolenic acid, jasmonic acid and, even more so, methyljasmonate, are highly effective inducers of tendril coiling in B. dioica. Methyljasmonate was most active when administered by air and, in atmospheric concentrations as low as 40-80 nM, induced a full free-coiling response with kinetics similar to mechanical stimulation. Even atmospheric levels as low as 4-5 nM methyljasmonate were still found to be significantly active. Methyljasmonate could be one of the endogenous chemical signals produced in mechanically stimulated parts of a tendril and, being highly volatile, act as a diffusible gaseous mediator spreading through the intracellular spaces to trigger free coiling of tendrils.

Abstract. The ultrastructure of epidermal cells of tendrils of Bryonia dioica Jacq. (Cucurbitaceae) was determined using microscopic, histochemical and immunochemical techniques with focus on the tactile blep, the mechanoreceptor of these cells. Tactile bleps resemble bordered pits in structure and probably in formation. They contain cytoplasm rich in endoplasmic reticulum, dictyosomes, mitochondria and microbodies. The cytoplasm is highly vesiculated and usually contains lipid-body-like structures. Cytoskeletal elements (microtubules, actin filaments) are uniquely arranged in the tactile blep, and chlorotetracycline-fluorescence analysis shows large amounts of membrane-associated calcium within the tactile blep. We propose a physically interconnected cytoskeleton-membrane device as the immediate force sensor and transducer which creates a primary intracellular signal, for which calcium is a likely candidate.

The touch‐induced free coiling response of Bryonia dioica tendrils is accompanied by the differentiation of supporting tissue at the ventral side of the organ, becoming the inner (concave) side of the coiled tendril. As part of this process, the Bianconi plate, a continuous sclerenchyma sheath stretching along the ventral face of the five bicollateral vascular bundles, becomes strongly lignified. During this reaction, the extractable activity of phenylalanine ammonia‐lyase in the tendrils increases four‐ to five‐fold, while the amount of PAL, as demonstrated by immunoblotting, remains unchanged. This touch‐induced process can also be elicited by airborne application of methyl jasmonate. The PAL inhibitor, 2‐aminoindan‐2‐phosphonic acid (AIP) completely inhibits both the touch‐ and methyl jasmonate‐induced deposition of lignin‐like material in the Bianconi plate, but has no effect on coiling. From these results, it can be concluded that the cessation of growth at the ventral side of a free‐coiling tendril is not due to induced lignification but rather, lignification seems to serve the function of increasing the mechanical strength of the coiled tendril.