Effects of subminimal temperature on physiology and ultrastructure of <i>Zea mays</i> embryo during germination

The effects of a subminimal temperature on germinating Zea mays kernels have been studied at the physiological and ultrastructural levels. After 72 h of germination at 16 °C, kernels were exposed to 4 °C for intervals ranging from 4 to 25 days and then returned to 16 °C. Resumption of growth of all the embryos occurred when the cold exposure was 6 or 8 days. When periods at 4 °C were longer than 8 days, a decrease in the percentage of embryos able to grow was observed; this was proportional to the length of cold exposure. After 26 days or more at 4 °C, all the embryos died. An ultrastructural study of the primary root cells showed that modifications occur in the cytoplasm and in the nucleolus. The nucleolus became predominantly fibrillar and unusual ribonucleoproteinic granules were frequently observed in and near the nucleolus organizer region. These changes were related to a strong decrease in transcription

Cytological study on water stress during germination of Zea mays

Kernels of Zea mays were subjected to dehydration treatment at various times during germination. Embryos from kernels dehydrated during the first 36 h of germination are resistant to dehydration and subsequently germinate earlier than controls. Dehydration of kernels germinated during 72h leads to an irreversible arrest of growth of the embryos. However, autoradiographic observations showed that these embryos are still able to incorporate [3H] uridine and probably [4-5-3H] lysine. Incorporation of [3H] thymidine does not occur. The effect of dehydration on root ultrastructure was studied. In embryos dehydrated after 24 h and 72 h of germination, condensation of chromatin is seen and association of elements of rough endoplasmic reticulum with vacuoles and glyoxysomes can be noted. These changes are reversible in drought-resistant embryos and irreversible in drought-sensitive embryos. However, more notable changes than those seen after 24 h can be observed in embryos dehydrated after 72 h of germination: mitochondria and proplastids can not be distinguished with certainty, glyoxysomes fuse and preferably dispose at the periphery of the cell. Rehydration of drought-sensitive embryos causes breakdown in plasma and nuclear membranes, which leads to the loss of cellular compartimentalization. Moreover, the chromatin remains definitively condensed and has lost its function of genetic regulation

Quantitative freeze-fracture study of plasmalemma and nuclear envelope of Zea mays root cells during early germination

Descriptive and quantitative observations of the plasmalemma and nuclear envelope of freeze-fractured root cells are reported for quiescent and early germinating maize embryos. The numerical density of particles exposed on the extracellular fracture faces of the plasmalemma increases significantly between 12 and 24 hr of germination while it remains unchanged on the protoplasmic fracture faces. The plasmalemma is significantly thicker after 24 hr of germination probably due partially to its enrichment in particles. Between 24 and 72 hr of germination there is a significant increase in the density of nucleopores. The fine structure of the nucleopores changes between 4 and 24 hr of germination. The first 24 hr of germination are also characterized by a spectacular rise in the density of particles of the two nuclear membranes. The results are discussed with respect to germination, particularly that of the maize embryo in which several cellular and molecular aspects have already been studied

First results of the EXE-kas development

The EXE-kas (= EXergy Efficient greenhouse) is an energy saving greenhouse that consists of an efficient dehumidification device (=vapour heat pump), Energy Balancing (EB) screens and an efficient CO2 generation system (CO2P). Two elements of this EXE-kas, namely the vapour heat pump and the EB day screens, are being developed in cooperation with industrial partners. The EB-day screen consist of a combination of 2 screens with higher light transmittance and improved thermal properties. The vapour heat pump consist of a heat mass exchanger in which air is dried through contact with a salt solution, and a mechanical vapour compression unit that concentrates the salt solution. In 2015 and early 2016, these devices were engineered and produced. In 2016 they will be tested in an experimental greenhouse of 720m². This presentation presents some practical development issues and the first results

The development of the EXE-kas

Different primary energy saving techniques for greenhouses have been tested in the past. Those systems were designed by using the first law. However, no attention was paid to the exergy destruction in the processes (second law). This exergy destruction is related to the driving potential of the processes and the mass/energy transfer quantity, and it determines the efficiency of the system. In this paper, different energy saving techniques for greenhouses are studied based on exergy analyses at the process level. Many of the studied techniques could be labelled as "less promising". Based on this assessment, our research team select an efficient dehumidification device (vapour heat pump) and EB (Energy Balancing)-screens as most promising. A greenhouse equipped with those techniques is named "EXE-kas" (Exergy Efficient greenhouse). The prospected dehumidification efficiency of an optimal designed vapour heat pump is around 10. The use of the EB-screens results in a near neutral energy balance of the greenhouse without heating

The development of the EXE-kas

Different primary energy saving techniques for greenhouses have been tested in the past. Those systems were designed by using the first law. However, no attention was paid to the exergy destruction in the processes (second law). This exergy destruction is related to the driving potential of the processes and the mass/energy transfer quantity, and it determines the efficiency of the system. In this paper, different energy saving techniques for greenhouses are studied based on exergy analyses at the process level. Many of the studied techniques could be labelled as “less promising”. Based on this assessment, our research team select an efficient dehumidification device (vapour heat pump) and EB (Energy Balancing)-screens as most promising. A greenhouse equipped with those techniques is named “EXE-kas” (Exergy Efficient greenhouse). The prospected dehumidification efficiency of an optimal designed vapour heat pump is around 10. The use of the EB-screens results in a near neutral energy balance of the greenhouse without heating