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.

Keywords: Calcium; Medicago sativa; Pisum sativum; Trifolium pratense; Vicia faba; forisome; sieve elements; sieve-element occlusion.

Figure 1.

Absolute numbers and percentage of forisome distribution at different locations (basal, central, apical) in sieve elements of A Vicia faba, B Medicago sativa, C Trifolium pratense and D Pisum sativum. Different letters indicate significant differences of the number of forisomes in this location. The forisome location was analysed with a Chi-square test, followed by multiple comparisons, while the familywise error rate was controlled by the Bonferroni correction.

Figure 2.

Dispersion and recondensation of forisomes in response to a remote heat stimulus. A Vicia faba, B Medicago sativa, C Trifolium pratense and D Pisum sativum. The forisomes are marked by asterisks; SE – sieve element; SP – sieve plate.

Figure 3.

Reactivity (dispersion and re-condensation) in response to a remote heat stimulus of basally located forisomes in intact Vicia faba, Medicago sativa, Trifolium pratense and Pisum sativum. A Percent of dispersed forisomes, B duration from burning until dispersion, C duration from dispersion until re-condensation and D duration from burning until re-condensation.