Kishore S. Rajput

Seasonal Behaviour of Vascular Cambium in Teak (Tectona Grandis) Growing in Moist Deciduous and Dry Deciduous Forests

Seasonal behaviour of vascular cambium in Tectona grandis L. f. growing in Moist Deciduous Forests (MDF) and Dry Deciduous Forests (DDF) of Gujarat State in Western India was studied for one annual cycle. In both the forests active cambial cell division and simultaneous differentiation of xylem and phloem started in June when the dormant shoot buds opened. In MDF cambial cell activity reached its peak in August-September and ceased in October; in DDF it ceased in November after reaching a peak in July-August. Maximum radial growth in trees of both forests occurred during the monsoon period. In both forests, phloem differentiation ceased before xylem differentiation. During dry months and the leafless periods the cambium remained dormant. Xylem mother cells next to the mature xylem in MDF underwent differentiation into xylem elements following the onset of periclinal divisions in March. In both forests, the seasonal anatomical changes associated with the cambium closely followed the phenology of the tree and local climatic conditions.

Thermostable xylanase production and partial purification by solid-state fermentation using agricultural waste wheat straw.

A locally isolated strain of Trichoderma harzianum was studied for production of xylanase (EC 3.2.1.8) using lignocellulosic substrates for solid-state fermentation. Among the different substrates used, wheat straw produced the highest yields (146 IU/ml). The influence of temperature, pH, moistening agents, moisture level, carbon sources, nitrogen sources, pretreatments and metal ions were evaluated with respect to xylanase production. Highest xylanase production was obtained using wheat straw after 12 days of incubation. Different substrate combination ratios and the effect of particle size were also checked against xylanase production. Maximum xylanase production was observed in a wheat straw/rice straw ratio of 1:1, with a particle size of 0.45–0.5 mm. Media supplementation with xylose as a carbon source in a ratio 1:5 (carbon source/substrate) gave maximum activity (157 IU/ml). Nitrogen supplementations from yeast extract produced xylanase activity of 141 IU/ml. Optimum xylanase production was observed at 30°C and pH 5.0. Xylanase production was enhanced in the presence of Ca2+ and Zn2+ ions. Ammonium sulfate fractionation (20–80% saturation) of partially purified xylanase yielded 76.5% of the enzyme with a 3.53-fold purification. The molecular weight of xylanase was found to be ca. 29,000 Da by SDS–PAGE.

Secondary growth in the stem of some species of Alternanthera and Achyranthes aspera (Amaranthaceae).

Secondary growth in Achyranthes aspera, Alternanthera polygamous, A. pungens, A. sessilis, and A. triandra was achieved by the development of a cambial variant resulting in successive rings of xylem and phloem. Each new cambium was developed at a distance about two to three cells external to the phloem produced by the previous cambium. The development of phloem was not synchronous in the species studied. Phloem development started either simultaneously with xylem or after the formation of a few xylem derivatives. In Achyranthes, xylem production started first followed by the development of phloem. Phloem mother cells differentiated into sieve tube elements, companion cells and axial parenchyma. Xylem was storied and exclusively composed of axial elements. Radial elements were absent in all the xylem rings of the stem. Vessels were angular and mostly solitary, but radial and tangential multiples were also observed occasionally. Xylem fibres were nonseptate and nucleated. Development of phloem and the rayless nature of the xylem is discussed.

Development of intraxylary phloem and internal cambium in Ipomoea hederifolia (Convolvulaceae)

Abstract In Ipomoea hederifolia L. (Convolvulaceae), internal/intraxylary phloem originated as isolated strands from the procambially derived cells after the formation of protoxylem and protophloem. Bands of internal phloem were apparent in the sixth internode after the development of metacambium. In the relatively thick stems several small arcs/segments of internal cambium ensues from the parenchyma cells between the protoxylem and internal protophloem. Though all the segments were active, some of them (two of them located opposite to each other) were relatively more active. Bidirectional differentiation of these segments gave rise to secondary xylem centrifugally and secondary phloem centripetally, resulting inverted vascular bundles. Rest of the internal cambium segments were unidirectional and formed only secondary phloem centripetally. Like external vascular cambium, the internal cambium was non-storied. Structurally, secondary xylem and phloem was composed of axial and radial system in which rays were mostly uni- to biseriate. Secondary xylem produced by the internal cambium was more or less similar to the xylem formed by the external successive cambia. Secondary phloem produced by the internal cambium was composed of sieve tubes, companion cells, axial and ray parenchyma cells. Simple sieve plates of internal phloem were mostly arranged on transverse end walls in contrast to compound and obliquely placed sieve plates of external phloem formed by the successive cambia.

CAMBIAL VARIANT AND XYLEM STRUCTURE IN THE STEM OF COCCULUS HIRSUTUS (MENISPERMACEAE)

Development of cambial variant and xylem structure were studied in the stem of Cocculus hirsutus (Menispermaceae). In the early stages of stem development several collateral vascular bundles are joined by interfascicular cambium resulting in the formation of a complete cambial cylinder. After functioning for two to three years the cambial ring ceases its activity. Subsequently a second ring of cambium is formed from the innermost cortical parenchyma cells. These parenchyma cells undergo periclinal divisions to give rise to cells that become lignified, abaxially, and cambial cells, adaxially. The cambial cells divide periclinally giving rise to individual vascular bundles with xylem and phloem. Later the cambium in each bundle is joined by interfascicular cambium. Subsequent cambia develop similarly resulting in the formation of successive rings of xylem and phloem. During the leafless condition, all the cambial rings are dormant, and flanked by mature xylem and phloem elements. With the sprouting of new leaves, either the existing outermost cambium reactivates or an entire new ring of cambium develops. The xylem is diffuseporous with indistinct growth rings. It is composed of fibre-tracheids, tracheids, vessel elements, libriform fibres, and parenchyma cells. Xylem rays are multiseriate, compound and heterocellular. Deformed libriform fibres and vessel elements commonly occur among the ray cells in all the successive rings of xylem. The length of fibres and the height and width of xylem rays increase gradually from the centre towards the periphery of the stem.

Pattern of delignification in Ailanthus excelsa Roxb. wood by Inonotus hispidus (Bull.: Fr.) Karst.

The pattern of delignification in Ailanthus excelsa Roxb. wood, naturally infected by Inonotus hispidus (Bull.: Fr.) Karst., was studied by light microscopy. Inonotus hispidus produced a typical pattern of soft rot decay even though it is grouped with white rot basidiomycetes. Fungal hyphae colonised all cell types of the secondary xylem but more damage was observed in xylem fibres. In the early stage, infection commenced on the cell wall corners and middle lamellae of the fibre wall without any pronounced effect on the primary and secondary wall layers. Delignification of fibre wall became apparent when all cell types became completely invaded by fungal hyphae. It started from within the lumina towards the middle lamellae, occurring initially in the immediate vicinity of hyphae growing on the luminal surface by forming an erosion trough. At an advanced stage of decay, localised degradation of lignin, cellulose and hemicellulose resulted in the formation of small cavities within the secondary walls (S2) of fibres. These cavities were never observed to contain any fungal hyphae. Though the vessels were resistant to infection, xylem rays and fibres were relatively less resistant to attack by I. hispidus. In severe infection, vessel lumens were found to be filled with sclerotic tissue which blocked them, resulting in complete collapse. The formation of cavities and the extent of cell wall damage are described in detail.

Nucleated Wood Fibres in Some Members of Combretaceae

The wood fibres retain their living protoplast in eleven species of five genera of the Combretaceae. Among the species studied, those of Anogeissus and Terminalia are trees while those of Calycopteris, Combretum and Quisqualis are large scandent shrubs. Living fibres with oval to oblong or fusiform shaped nuclei were found among all the species but their occurrence is more persistent in trees than in scandent species. The fibres are septate, thick-walled with narrow lumen and possess slitlike simple pits. In Combretum ovalifolium prismatic crystals frequently co-occur with the nucleus in the same compartment of the fibres. The possible significance of living fibres is discussed.

Wood Anatomy and the Development of Interxylary Phloem of Ipomoea hederifolia Linn. (Convolvulaceae)

In Ipomoea hederifolia Linn., stems increase in thickness by forming successive rings of cambia. With the increase in stem diameter, the first ring of cambium also gives rise to thin-walled parenchymatous islands along with thick-walled xylem derivatives to its inner side. The size of these islands increases (both radially and tangentially) gradually with the increase in stem diameter. In pencil-thick stems, that is, before the differentiation of a second ring of cambium, some of the parenchyma cells within these islands differentiate into interxylary phloem. Although all successive cambia forms secondary phloem continuously, simultaneous development of interxylary phloem was observed in the innermost successive ring of xylem. In the mature stems, thick-walled parenchyma cells formed at the beginning of secondary growth underwent dedifferentiation and led to the formation of phloem derivatives. Structurally, sieve tube elements showed both simple sieve plates on transverse to slightly oblique end walls and compound sieve plates on the oblique end walls with poorly developed lateral sieve areas. Isolated or groups of two to three sieve elements were noticed in the rays of secondary phloem. They possessed simple sieve plates with distinct companion cells at their corners. The length of these elements was more or less similar to that of ray parenchyma cells but their diameter was slightly less. Similarly, in the secondary xylem, perforated ray cells were noticed in the innermost xylem ring. They were larger than the adjacent ray cells and possessed oval to circular simple perforation plates. The structures of interxylary phloem, perforated ray cells, and ray sieve elements are described in detail.

Cambial Activity and Wood Anatomy in Prosopis Spicigera (Mimosaceae) Affected by Combined air Pollutants

Seasonal cambial activity and xylem anatomy were studied in Prosopis spicigera Linn. (Mimosaceae) growing under the influence of combined air pollutants. Cambial cell division and differentiation of secondary xylem began in April, reached a peak in July–August and ceased in October in trees (normal) growing in a relatively unpolluted locality. In contrast, in trees (affected) growing near a fertilizer complex, the initiation of cambial activity was delayed by one month and the cambium ceased to divide in September. Considerable variations were noticed in the structure and arrangement of xylem derivatives between affected and normal trees. The vessel lumen diameter was reduced and vessel frequency was significantly higher in the affected trees. Axial parenchyma was aliform to confluent in normal trees compared to mainly vasicentric parenchyma with heavy accumulation of tannin contents in affected trees. Cambial activity and xylem development did not show any correlation with the phenology of affected trees.

Development of Intra- and Interxylary Secondary Phloem in Coccinia indica (Cucurbitaceae)

Stem anatomy and the development of intraxylary phloem were investigated in six to eight years old Coccinia indica L. (Cucurbitaceae). Secondary growth in the stems was achieved by the normal cambial activity. In the innermost part of the thicker stems, xylem parenchyma and pith cells dedifferentiated into meristematic cells at several points. In some of the wider rays, ray cells dedifferentiate and produce secondary xylem and phloem with different orientations and sometimes a complete bicollateral vascular bundle. The inner cambial segments of the bicollateral vascular bundle (of primary growth) maintained radial arrangement even in the mature stems but in most places the cambia were either inactive or showed very few cell divisions. Concomitant with the obliteration and collapse of inner phloem (of bicollateral vascular bundles), parenchyma cells encircling the phloem became meristematic forming a circular sheath of internal cambia. These internal cambia produce only intraxylary secondary phloem centripetally and do not produce any secondary xylem. In the stem, secondary xylem consisted mainly of axial parenchyma, small strands of thick-walled xylem derivatives, i.e. vessel elements and fibres embedded in parenchymatous ground mass, wide and tall rays along with exceptionally wide vessels characteristic of lianas. In thick stems, the axial parenchyma de-differentiated into meristem, which later re-differentiated into interxylary phloem. Fibre dimorphism and pseudo-vestured pits in the vessels are also reported.