When plants are exposed to HM (Al, Cd, Cu etc.), they accumulate
callose at plasmodesmata causing alteration in their permeability (De Storme and Geelen, 2014).
After 15-20 min, it is possible to observe a cone-shaped
callose thickening surrounding the perforation region of the outer periclinal wall of the epidermal cell.
This suggested that malate, by retaining [Fe.sup.3+], increases the action of LOW PHOSPHATE ROOT 1 (LPR1) on [Fe.sup.2+] reduction, triggering
callose synthesis and consequent inhibition of cell division (MORA-MACIAS et al., 2017), as well as stimulating peroxidases that cause cell wall stiffening, reducing elongation (BALZERGUE et al., 2017).
glycines, including phloem protein coagulation and
callose accumulation [Tjallingii 2006), deposition of lectins (Bostwick et al.
It has been demonstrated that in phytoplasma-infected plants,
callose deposition is a common phenomenon and is associated with the accumulation of carbohydrates [75], which can accumulate free hexoses and further repress the synthesis of chlorophyll a-b binding proteins [54].
It has been shown that chitosan elicits defense mechanisms in plants through induction of glucanases, chitinases, phenolic compounds, terpenoids, PR proteins, protease inhibitors, and compounds associated with oxidative burst, lignification and
callose deposition (Bautista-Banos et al., 2006; Franco and Iriti, 2007; Mandal and Mitra, 2007; Hadwiger, 2013; Mejia-Teniente et al., 2013).
Moreover cambium consists of oligo- and polysaccharides such as galactooligosaccharides, cellulose, lignin, and
callose.
These defense mechanisms include: strengthening of the cell wall through lignin, suberin and
callose deposition as well as by the synthesis of phytoalexins which are toxic to bacteria and fungi by producing Pathogenesis-Related (PR) proteins like chitinases, b-1,3-glucanases, and thaumatin-like proteins (Bowles, 1990).
According to Kays (1991), the increase in respiratory rate in response to injury is related to the healing process, with the formation of lignin, suberin and in some cases
callose. Montero et al (2010) found in 'Fuji' and 'Gala' apples damaged by impact and compression, increased respiratory rate in the first six hours after damage.
Observations by Parthasarathy (1968) described oil palm trunks as having '
callose and outgrowths of adjacent parenchyma cells which is proof of an internal deterioration of the trunk and therefore a decrease in activity'.