Comparison of intracellular location and stimulus reaction times of forisomes in sieve tubes of four legume species

Abstract

Forisomes in legumes are responsible for fast sieve-element occlusion in response to injury to the vascular system. This prevents uncontrolled leakage of phloem sap and protects against invasion of pathogens. Here we compared forisomes of four different legumes (Pisum sativum, Vicia faba, Trifolium pratense and Medicago sativa) by their location (basal, central, apical) in the sieve element and reactivity to a distant heat stimulus. In each species, the majority of forisomes was located basally. Yet, we found differences in intracellular location: forisomes are distributed more evenly in the sieve elements of Pisum. After burning, basally located forisomes of the four species reacted with dispersion, followed by a spontaneous recondensation with similar reaction times. The results suggest universal forisome behaviour in fabacean species.

Species-Specific and Distance-Dependent Dispersive Behaviour of Forisomes in Different Legume Species

“…M. sativa 1.0–2.0 cm; P. sativum 0.7–3.2 cm; T. pratense 0.5–3.8 cm; V. faba 1.1–6.5 cm. As forisomes at different locations (basal, central, apical) in the SE show different dispersion behaviours and times, only forisomes located proximally (basally) in SEs were considered for experiments [ 71 ], and each plant was used only once.…”

“…Microscopic examination of forisomes in intact SEs was largely identical to the established method described by Knoblauch and van Bel [ 17 ] and Furch et al [ 71 ]. Cortical cell layers were removed with a razor blade from the lower site of the midvein down to the phloem so that intact SEs were exposed.…”

Pea Aphid (Acyrthosiphon pisum) Host Races Reduce Heat-Induced Forisome Dispersion in Vicia faba and Trifolium pratense

“…Plants were handled in a manner so as not to dislodge feeding aphids from the plants. For in vivo observations of forisome reactions, the phloem was exposed by removing the cortical cell layers from the lower side of the midvein with a razor blade as described previously [13,80]. The leaf was then fastened upside down onto an objective slide with double-sided adhesive tape.…”