Introduction

The liquids and deposits of guttation on hydathodes consist of organic as well as inorganic constituents that vary from time to time. In this context, stem exudation obtained through decapitation for chemical analysis can be equated, by and large, to guttation fluid. Similarly, xylem-sap constituents can be likened to guttation fluid constituents as well. The composition of these liquids is determined by the age, physiological activity, plant species and varieties, as well as the solute composition and concentration of the medium from which the plant absorbs. Most of the guttate and solute samples obtained from hydathodes were not collected under controlled conditions, and so, their composition test results, at best, indicate general trends. The composition of the guttated liquid seems to vary from pure water to a dilute solution of organic as well as inorganic solutes that constitute around 0.05–0.5 percent of the liquid. Curtis (1943) showed that guttate obtained from squash, cabbage, tomato, and cucumber are some of the best examples of the general order of magnitude of solute concentration and guttate's composition. Nearly 50 percent of the solute was organic in nature, which ranged from 600 to 2500 mg L−1. The osmotic potential of guttated liquid obtained from leaves of cotton plants varied from −0.051 to −0.091 MPa for plants growing in the usual concentration of nutrient solution, whereas it was −0.013 MPa for plants grown in a dilute solution (Eaton 1943). Following heavy application of fertilizer to a lawn, the leaves of the grass were encrusted with a deposit of glutamine left by the evaporation of guttated liquid, and the leaves of some species of Saxifraga usually become coated with calcium salts (Curtis 1943). In this chapter are described the salient features of the chemistry of guttation fluids in some detail, which carry immense agricultural, pharmaceutical, nutriceutical, therapeutical, cosmeceutical, and commercial significance (Rybicki 2009).

Organic constituents of guttation fluids

Guttation fluids are known to carry several different organic materials such as sugars, amino acids, amides, purines, pyrimidines, reductants, various kinds of proteins (such as simple proteins, recombinant proteins, transporter proteins, and signal transduction proteins), enzymes (such as isoprenyl transferase, peroxidases, ATPases, and dehydrogenases), antibodies, ATP, mRNA, lipophilic materials, volatile oils, herbicides, insecticides, fungicides, alkaloids, and toxins (Fischer et al. 2004; Ma et al. 2005; Twyman et al. 2005) (Figure 5.1, Table 5.1).