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Articles by S. Sikolia
Total Records ( 5 ) for S. Sikolia
  S. Sikolia , E. Beck , J.I. Kinyamario , J.C. Onyango and G. Ouma
  δ13C values of the Centrospermeae species are presented. 69.5, 28.45, 1.25 and 0.8% of the total species are C3, C4, C3-C4 and CAM photosynthetic species. The δ13C values are species dependent. δ13C values for the C3 range from -21.16 to -30.28‰ while the C4 species vary from -10.60 to -16.55‰. An exceptional δ13C value of -32.28 is reported for Chenopodium capitatum. δ13C value for the CAM species vary from -16.00 to -18.50‰. C3-C4 species includes Mollugo nudicaulis, Portulacaria afra and Portulaca sp. nov. with δ13C values -25.89, -20.93 and -15.66‰, respectively. Temperature and precipitation are the dominant causal climatic factors that influence the distribution of the C3 and C4 species inversely and by extension the δ13C values along the altitude. Other climatic factors act synergistically. A difference in the δ13C values is a biochemical dual function of the Rubisco and suberized lamella anatomical structural organization. The occurrence of some C4 species in the unusual high altitude includes Melandrium nordiflorum and Silene abyssinica and may be due to the Pyruvate Phosphate Dikinase (PPDK) enzyme functional activity. Ecological significances of the δ13C values are discussed.
  S. Sikolia , J.C. Onyango , E. Beck and J.I. Kinyamario
  Two hundred and seventy eight species of the Centrospermeae were collected at different sites in Western Kenya representing gradients of altitude and aridity. Climate data were obtained from meteorological research stations. Species were examined for C3 or C4 photosynthesis using the anatomical Kranz syndrome, δ13C values and carbon dioxide compensation points. C4 photosynthesis is a feature of modern members of dicotyledoneae is of multiple evolutionary origins. It evolved independently in members of the same family and was found in one to several genera and then often only with two to three species. C4 species are concentrated in lowland habitats subjected to high temperature, low precipitation and high evaporation. High δ13C values is associated with low water availability which is a physiological syndrome and also a feature of saline habitats. The C3 representatives of the Centrospermeae dominate in more moist and colder habitats, especially at higher altitudes. Only a few C4 species occur at high altitudes (3000-4000 m) namely Sagina gallica, Silene abyssinica and Melandrium nordiflorum. The transition zone between C3 and C4-dicot is rather narrow between 1500 to 1700 m and thus much lower than that recorded for the monocots (2000-2200 m). The general pattern of δ13C values distribution along the altitudinal gradient show that the values of -10.60 to -16.55, -17.75 to -18.87 and -18.89 to -32.42‰ that corresponds to altitudinal ranges, 0-1500, 1550-1700 and 1800-4200 m, respectively. The low altitudes are associated with drought and high temperatures. C4 and C3 dicot species can be intercropped to increase bioproductivity for the betterment of the flora and fauna in the semi-arid and arid ecosystem. C4-species are potential candidates for exploitation in the agroforestry systems especially for long-term management programmes. The present study may also be relevant for better understanding of global change with respect to the diversity of photosynthetic pathways, herbivory and vegetation dynamics.
  S. Sikolia , E. Beck and J. C. Onyango
  The present studies on carbon dioxide compensation point () considered species from tropical semi-arid, snowline and saline ecosystems. The aim of the study was to establish the ecological range of the CO2 compensation point of species in the semi-arid/arid, snowline/or saline conditions. Secondly, to determine the effect of biomass on the rate of carbon dioxide assimilation in relation to the ecological efficiency of the C3 and C4 photosynthetic pathways. Four and six-seven week old plants were used to assimilate carbon dioxide in the gas chamber until a constant reading was attained by Infra Red Gas Analyzer (IRGA). The carbon dioxide uptake concentrations (assimilations) were continuously measured by pumping a stream of the air through a closed gas tight, circuit with IRGA while temperature and light intensity and previous growth conditions were maintained constant. The dry weight of the plant was measured using a digital balance after the experiment. The CO2 compensation points of the C4 plants vary between 8-20 ppm. The CO2 compensation points of the C3 plants vary between 40-60 ppm. The age and biomass of the plant influenced the rate of carbon dioxide assimilation in the C4 species and C3 species. The C4 plant attained the CO2 compensation point faster than C3 plant under the same physiological conditions. The C4 plant photosynthesized below 40 ppm of carbon dioxide concentration. The C3 plant ceased carbon dioxide assimilation below 40 ppm of carbon dioxide concentration. Thus, an ideal ecological canopy set-up should consist of a C4 over storey and a C3 under storey for efficient photosynthetic performance and yield. Potential C4 overstorey species including Amaranthus species and Kochia scoparia, should be intercropped with potential C3 understorey species like Chenopodium album and Phytolaca dioica by farmers and horticulturalists in Agriculture. The intercropping practice is economical, viable and apt in agroforestry systems, especially in the semi-arid and saline conditions socialized by nomadic tribes in Kenya. Perkerra irrigation project can act as satellite agroforestry research station, including Kerio valley and Turkana regions.
  S. Sikolia and P. Ochora
  A trilocular ovary possesses several anatropous, tenuinucellate and bitegmic ovules on the axile placenta. Selective callose deposition in cell walls and effects of integumentary directional tension (or stress) forces during first meiotic division and natural competition between dyads exists. Micropylar dyad cell degenerates; shift in nutrient supply at megagametogenesis relates to the degeneration of the primary chalazal nucleus. Primary micropylar nucleus undergoes two free nuclear (mitotic) divisions producing four nuclei that alone organize a four-celled female gametophyte consisting of two synergids, a large central egg cell and a polar cell. Filiform apparatus are present in the synergids. Female gametophyte development is of the monosporic category, Apinagia type, form B; syngamy occurs. The cell walls of nucellar cells fails to resist acropetal net tension force of the inner integument, disorganize, break and release naked protoplast in the cavity formed resulting in a structure referred as nucellar plasmodium; role of lytic enzymes is pointed out. Nucellar plasmodium organizes during post-fertilization period in Trisicha trifaria of the Tristichoideae (Podostemaceae).
  S. Sikolia and J.C. Onyango
  This study aims to elucidate the ontogeny and organization of the female gametophyte. Further, provide evidences for the strike phenomenon in the Podostemaceae. The female gametophyte ontogeny in Inversodicraea bifurcata Engl. I. keniensis sp. nov. Nagendran et Sikolia conforms to the Apinagia type of the monosporic category. The primary chalazal nucleus degenerates at the two-nucleate stage. The strike phenomenon met in the family is discussed. The organized female gametophyte is four-nucleate, four-celled and consists of two pear shaped synergids, a large central egg cell and a polar cell. Filiform apparatus are present in the synergids. Based on the female gametophyte ontogeny, there are no antipodal cell(s). Earlier reports of double fertilization are not confirmed, but only single fertilization take place in the family. The nucellar plasmodium is rationalized on its organization and ontogeny and is formed before fertilization in Inversodicraea. Effects of tension force and lytic enzymes during nucellar plasmodium organization and its ultimate significance are discussed.
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