Molecular adaptation within the coat protein-encoding gene of Tunisian almond isolates of Prunus necrotic ringspot virus

The sequence alignments of five Tunisian isolates of Prunus necrotic ringspot virus (PNRSV) were searched for evidence of recombination and diversifying selection. Since failing to account for recombination can elevate the false positive error rate in positive selection inference, a genetic algorithm (GARD) was used first and led to the detection of potential recombination events in the coat protein-encoding gene of that virus. The Recco algorithm confirmed these results by identifying, additionally, the potential recombinants. For neutrality testing and evaluation of nucleotide polymorphism in PNRSV CP gene, Tajima’s D, and Fu and Li’s D and F statistical tests were used. About selection inference, eight algorithms (SLAC, FEL, IFEL, REL, FUBAR, MEME, PARRIS, and GA branch) incorporated in HyPhy package were utilized to assess the selection pressure exerted on the expression of PNRSV capsid. Inferred phylogenies pointed out, in addition to the three classical groups (PE-5, PV-32, and PV-96), the delineation of a fourth cluster having the new proposed designation SW6, and a fifth clade comprising four Tunisian PNRSV isolates which underwent recombination and selective pressure and to which the name Tunisian outgroup was allocated.     

A Note on the Ontogeny of Cross Veins in Digitaria eriantha

The small cross veins that link the longitudinal bundles arisefrom single files of the ground meristem. The tangential divisionsof the cross vein initial produce two vascular parenchyma cellsand two conducting elements. Digitaria eriantha, ontogeny, cross vein, tracheary element, sieve element     

Leaf Ontogeny in Digitaria eriantha

The shoot apex consists of two layers, the dermatogen and thehypodermis. The leaf primordia arise through periclinal divisionswithin these two layers on the side of the apex. Further divisionsof the dermatogen push the little protuberance upward and togetherwith divisions the hypodermis add internal tissues of the youngleaf. When the median and lateral bundles of the primordia arisein Digitaria eriantha they are isolated from the vascular supplyof the rest of the plant. The median strand, the first to form,and the first order laterals form at the disc of insertion ofthe primordium. The other laterals form higher up in the primordium.These strands extend both acropetally and basipetally to linkwith the vascular supply of the rest of the plant. Digitaria eriantha, apical meristem, leaf primordium, vascular bundle, orange G, tannic acid, iron alum     

A Comparative Study of the Structure-Function Relationship of Cross Veins in Leaves of Digitaria eriantha and Zea mays

Ultrastructural and functional differences between the crossveins of Digitaria eriantha and Zea mays were investigated.Cross veins of both genera possess similar conducting tissues,namely one tracheary element and one sieve cell. In Digitariaeriantha these conducting elements are associated with onlytwo parenchyma cells, and, those in Zea mays are completelysurrounded by chJorenchyma cells. The protein ribulose 1,5-bisphosphatecarboxylase/oxygenase (rubisco) was used as a probe for CO₂fixation sites by comparing its distribution in the varioustissue types in the leaves of the two genera. The protein wasfound to be equally and uniformly distributed in the stromalregions of the chlorenchyma sheath cell chloroplasts of longitudinalveins of both genera. The chlorenchyma sheath cells in crossveins of Zea mays show a similar distribution of the enzymeas the longitudinal bundles. However, this enzyme was shownto be absent in the cross vein parenchyma cells of Digitariaeriantha and in the mesophyll cells of both genera. Cross veins, immuno-gold labelling, ribulose 1,5-bisphosphate carboxylase/oxygenase, Digitaria eriantha, Zea mays