Evaluation of the specificity of lectin binding to sections of plant tissue

Specificity of widely used lectins as probed with oligosaccharide and plant polysaccharide arrays

Glycan-binding specificity was studied for Jacalin, RCA 120, SBA, PHA-L, PHA-E, WGA, UEA, AAL, LTL, LEL, SNA, DSA, LCA, MAH and Con A, lectins widely used in histochemistry. Oligosaccharide- and polysaccharide-based glycan arrays were applied. Expected specificity was confirmed for only 6 of the 15 lectins and the glycan binding profiles of some lectins were dramatically broader than generally accepted. WGA, LEL and DSA known as chitooligosaccharide-specific, were unexpectedly polyreactive, binding to other glycans with the same affinity as to chitobiose, ABH antigens and oligolactosamines (unsubstituted and sialylated). SBA, in addition to expected binding to glycans with terminal GalNAcα, also had high affinity for the GM1 ganglioside. MAH demonstrated much higher affinity to a variety of sulfated glycans compared to Neu5Acα2-3Galβ1-3GalNAcα. Contrary to the common view, LCA demonstrated the maximum binding to (GlcNAcβ1-2Manα1)2-3,6-Manβ1-4GlcNAcβ1-4GlcNAc N-glycan, while it had no interaction with corresponding Gal or Neu5Ac terminated versions. This observed polyreactivity of some lectins casts doubt on their use in accurately determining the presence of a specific glycan structure by histochemical studies. However, comparisons of sera from healthy and diseased individuals with help of a lectin array can easily establish differences in glycosylation patterns and presumptive glycan identities, which can later be clarified using more accurate methods of structural analysis.

The epidermal surface of the maize root tip: I. Development in normal roots

The surface of the meristematic epidermis of maize roots is tri-partite. A helicoidal primary wall follows the contours of the tops of the columnar epidermal cells and is continuous with their buttressed anticlinal walls. Two overlying layers form a smooth covering over the root which obscures the cell outlines. This compound surface is similar architecturally to outer epidermal surfaces of shoots. The two outer layers are distinct structurally and in their staining properties from the wall and are together here referred to as the pellicle. Both pellicle layers are fibrillar but not helicoidal. Their development begins in the boundary between the cap and the root proper and they reach maximum thickness over the meristematic region. The outer layer then disintegrates and is absent from the elongation zone. The inner layer thins irregularly as the columnar cells elongate to their final tabular form and usually persists only over the groove above anticlinal walls and at the base of root hairs. The cell wall thins to about half its maximum thickness during this elongation. Emerging root hairs broach the pellicle and the original primary wall. Remnants of both these layers form a short, tight collar at the base of each hair; this collar adheres to the primary wall of the hair which is continuous with a new, thin wall which is formed interior to the original outer wall of the parent cell. Failure to recognize the complex structure and transitory nature of the epidermal pellicle has led to confusion in the literature regarding the nature of root-surface and rhizosphere mucilaginous components and their origin. These interpretations are compared with those arising from this study.

The use of fluorochromes in the cytochemical characterization of some phytoflagellates

Sixteen fluorochromes were tested for the cytochemical characterization of two dinoflagellates (Amphidinuim carterae, Prorocentrum micans) and one chlorophycean flagellate (Dunaliella tertiolecta). Depending on the fluorochrome used, various cellular components (including the plasma membrane, thecal plates, pusule, trichocysts, nucleus, lipid bodies and vacuoles) were revealed. The different colours obtained from single or double fluorochrome staining enabled the differentiation and identification of most cellular components. Protoplasmic staining with Fluorescein diacetate suggested the occurrence of esterases in the three phytoflagellates. Rhodamine B, Neutral Red, FluoroBora P and Nile Blue revealed extensive occurrence of lipoid bodies in A. carterae, but Nile Blue showed considerable difference from the other stains in the inclusion size and intracellular location of these bodies. Chlortetracycline binding, and its inhibition by the Ca2+ionophore A23187, indicated that the plasma membrane, pusule system and trichocysts contain sites of Ca2+ binding. Calcofluor White ST proved superior to Congo Red and Lucifer Yellow in elucidating structural details of the thecal plates of P. micans. While Acridine Orange revealed the presence of surface-coat acidic polysaccharides, the fluoresceinated lectins established their glycoconjugate nature in all the three flagellates. Possible mechanisms of fluorochrome uptake are discussed.