Adaptive Anatomical Structure for Nastic Movement in Mimosa Pudica L

In order to study the adaptive anatomical structures during nastic movement of Mimosa pudica L., anatomical structures of main pulvinus, common petioles, rachis and leaflets were compared with Albizia julibrissin Durazz. (taken as control). The anatomical structures of main pulvinus and common petiole of M. pudica were different from that of A. julibrissin. Upon stimuliti, the protoplast volume of M. pudica in the lower cortical parenchyma cells become smaller than that in upper ones, a feature seldom found in A. julibrissin. There were found many reticulate lacunas on the two side of adaxial petiole of M. pudica, but nil in A. julibrissin. Similarly some ill developed lacunas were found in the pulvinus of rachis and leaflet of M. pudica, but absent in A. julibrissin. It appears that reticulate lacunas in common petiole of M. pudica are responsible for its strong nastic movement. The main sensitivity position lies at the base of common petiole, where the lower cortex is more sensitive than the upper cortex, and the ordinal sensitivity positions are rachis and leaflets. Introduction The great curiosity of Mimosa pudica L. (Fabaceae) is that the compound leaves fold inward and droop when touched, warmed, blowed, shaken or traumatic, re-opening minutes later (Roblin 1979, Pierrette and Bonnemain 1978, Milne and Beamish 1999). The leaves also droop at night, and when exposed to rain or excessive heat. The response may be defensive against herbivorous insects, leaching loss of nutrients, or desiccation (Nilesh et al. 2009). Albizia julibrissin Durazz. is also widely known as “Mimosa” and “Persian silk tree”. Although once included in Mimosa, it has not the nastic movement like M. pudica (http://gardens.co.nz/PlantoftheWeek.cfm? NLID=96). For M. pudica many opinions or hypothesis on the causes of leaf movements were proposed, which are: (i) Osmoregulation hypothesis: it was thought that the rapid bending movement of the main pulvinus of M. pudica is caused by a sudden loss of turgor pressure (Pfeffer 1905) and leaf movements occurred due to the transfer of K, Cl, H, accompanied with the change of water and osmotic pressure (Fromm and Eschrich 1990, Salisbury and Ross 1992). (ii) Ion channel hypothesis: Ca as second messenger played important role in message transfer of plant cells. Some authors thought that the pulvinus and leaf movements were correlated with Ca transmembrane conductance (Toriyama and Jaffe 1972, Roblin and Fleurat-Lessard 1984, Schwartz 1985). (iii) Cytoskeleton hypothesis: some thought it was actin filaments that took part in the stimulative movements of M. pudica (Fleurat-Lessard et al. 1988). Although Fleurat-Lessard and Roblin (1982) reported the histocytology of M. pudica, but seldom comparative study was reported on each joint points of pulvinus, petiole, rachis and leaflet in M. pudica. The objective was to study the adaptive mechanism between the movement function and the anatomical structures of M. pudica taking A. julibrissin as a control. *Author for correspondence: .