4 Discussion

The water content in seeds with impermeable seed coats has important implications for germination, because impermeable coats prevent germination until environmental conditions promote water absorption by seeds followed by germination (Kestring et al., 2009; Ribeiro et al., 2015). This study found a reduction in the seed germination of J. curcas, according to seed water imbibition. It is supposed that seeds need a small amount of water for promote the germination because the water imbibition had linearly decrease the germinability and increase its mean germination time, two parameters related to the seed vigor. This phenomena was previously reported in other species, like corn (Matthews and Hosseini, 2006), rice (Ruttanaruangboworn et al., 2017) castor oil (Ribeiro et al., 2015) and Astrophytum species (Sánchez-Salas et al., 2012); however, in contrast of Mimosa bimucronata (Kestring et al., 2009) a floodplain species, where the water uptake sharply increases the seed germination. Also, it was observed during the time line of the experiment there was an increase in EC that reflect in lost the seed germinability from seed steeping in water from 2 to 24 hours.

The seeds used in this experiment were stored in dry environments and hence had very low levels of metabolism. We argue that, during seed imbibition, they swell and metabolic activity increases. Hydration of tissue components during imbibition takes place in a not controlled way so that the reconstruction of internal structures of the cells and organelles were affected. So, leakage of stored components and enzymes, colouring, cracking or absence of cotyledons, and overall damage to the hypocotyl may occur during germination (Hobbs and Obendorf, 1972; Pollock et al., 1969). The amount of the constituents of the leaked depended unequivocally on the initial water content of seeds; the lower moisture in seed at the initial water content show more leakage occurring in seeds with low water contents, below 10% in soybeans seeds (Ishida et al., 1988). This damage takes place in the early stages of imbibition (Parrish and Leopold, 1977). This indicates that membrane functions are restored, even though the activities of respiration and metabolism are restricted. Water molecules are semi-bound and mobile water necessary for metabolism is deficient for moisture contents between 12-24% (Koizumi et al., 2008). According to these, the loss of viability can be explained base on the initial seed water content of the seeds used in the experiment because they had an initial moisture around 8%, that is low value compared with the moisture at harvest that is around 18% (Marcelo Francisco Pompelli et al., 2010); a possible explanation could be the lost of water by storage condition of the seed for the experiment. In other crops like soybean seeds, water content is usually 10 to 20% at harvest and falls further during storage, seed water contents below 10% were shown to be desirable for long period storage because seeds stop their biological activities and the stored materials are consumed at a minimum level (Windauer et al., 2007). J. curcas seeds after 24 hour of imbibition increases 6.5 times its initial moisture as reported in soybean seeds (Ishida et al., 1988). Dried seeds can raise their water content to a certain level, two or three times the dry weight, and this rapid increase of water is often accompanied by some deterioration of the tissues, called imbibitional damage. This damage is expressed as a reduced rate of germination and reduced yield of surviving plants (Ishida et al., 1988). It can be the reason in decrease in the germination percentage in this research. It was reported that soybean seeds with the water content below 13% suffered seriously from imbibitional damage while those above 17% did not, where respiration and metabolic activity rapidly increase with the increase of moisture content (Ishida et al., 1988; Vertucci and Leopold, 1984). Imbibition damage results from the rapid entry of water into the cotyledons during imbibition, leading to cell death and high solute leakage from the seeds (Powell et al., 1986) and the extensive loss of cellular material and enzymes from the seeds (Duke and Kakefuda, 1981; PowellL and Matthews, 1981) indicates extensive membrane disruption. The electrical conductivity was related to seed water content and the germination for this reason EC tests has been applied to detect vigor differences in many other grain legumes and indeed some other species (Hampton and Tekrony, 1995; Moncaleano-Escandon et al., 2013). The conductivity will increase as the laboratory germination falls, in addition to the reduced ability of germination seeds to retain cell contents (Matthews and Hosseini, 2006). Reports on pea lots, the EC readings for lots have been found to relate significantly to field emergence (PowellL and Matthews, 1981; Thornton et al., 1990).

To alleviate the effects of imbibition damage as a result of the increase in the water content of seeds, a slow and controlled hydration is essential as the first step in the reactivation of metabolic processes in dry seed (Vertucci and Leopold, 1984) leading an increase in the germination and growth ability. The EC vigor test would be developed and standardized for these species (Abdullah et al., 1991; Powell, 1986; Yaklich and Kulik, 1979). Furthermore, it was reported than the relationship between field emergence and EC turned out to be not only interesting, but useful in practical seed technology (Matthews and Powell, 2006) as present in these work for J. curcas.

References

Kestring, D., Klein, J., Menezes, L.C.C.R. de, Rossi, M.N., 2009. Imbibition phases and germination response of mimosa bimucronata (fabaceae: Mimosoideae) to water submersion. Aquatic Botany 91, 105–109. https://doi.org/10.1016/j.aquabot.2009.03.004

Ribeiro, P.R., Willems, L.A., Mudde, E., Fernandez, L.G., Castro, R.D. de, Ligterink, W., Hilhorst, H.W., 2015. Metabolite profiling of the oilseed crop ricinus communis during early seed imbibition reveals a specific metabolic signature in response to temperature. Industrial Crops and Products 67, 305–309. https://doi.org/10.1016/j.indcrop.2015.01.067

Matthews, S., Hosseini, M.K., 2006. Mean germination time as an indicator of emergence performance in soil of seed lots of maize (zea mays). Seed Science and Technology 34, 339–347. https://doi.org/10.15258/sst.2006.34.2.09

Ruttanaruangboworn, A., Chanprasert, W., Tobunluepop, P., Onwimol, D., 2017. Effect of seed priming with different concentrations of potassium nitrate on the pattern of seed imbibition and germination of rice ( oryza sativa l.). Journal of Integrative Agriculture 16, 605–613. https://doi.org/10.1016/s2095-3119(16)61441-7

Sánchez-Salas, J., Jurado, E., Flores, J., Estrada-Castillón, E., Muro-Pérez, G., 2012. Desert species adapted for dispersal and germination during floods: Experimental evidence in two astrophytum species (cactaceae). Flora - Morphology, Distribution, Functional Ecology of Plants 207, 707–711. https://doi.org/10.1016/j.flora.2012.08.002

Hobbs, P.R., Obendorf, R.L., 1972. Interaction of initial seed moisture and imbibitional temperature on germination and productivity of soybean. Crop Science 12, 664. https://doi.org/10.2135/cropsci1972.0011183x001200050033x

Pollock, B., Roos, E., Manalo, J., 1969. Vigor of garden bean seeds and seedlings influenced by initial seed moisture, substrate oxygen, and imbibition temperature. Journal of the American Society for Horticultural Science 94, 577–584.

Ishida, N., Kano, H., Kobayashi, T., Yoshida, T., 1988. Analysis of physical states of water in soybean seeds by NMR. Agricultural and Biological Chemistry 52, 2777–2781. https://doi.org/10.1271/bbb1961.52.2777

Parrish, D.J., Leopold, A.C., 1977. Transient changes during soybean imbibition. PLANT PHYSIOLOGY 59, 1111–1115. https://doi.org/10.1104/pp.59.6.1111

Koizumi, M., Kikuchi, K., Isobe, S., Ishida, N., Naito, S., Kano, H., 2008. Role of seed coat in imbibing soybean seeds observed by micro-magnetic resonance imaging. Annals of Botany 102, 343–352. https://doi.org/10.1093/aob/mcn095

Pompelli, M.F., Rocha Gomes Ferreira, D.T. da, Silva Cavalcante, P.G. da, Lima Salvador, T. de, Hsie, B.S. de, Endres, L., 2010. Environmental influence on the physico-chemical and physiological properties of jatropha curcas seeds. Australian Journal of Botany 58, 421. https://doi.org/10.1071/bt10102

Windauer, L., Altuna, A., Benech-Arnold, R., 2007. Hydrotime analysis of lesquerella fendleri seed germination responses to priming treatments. Industrial Crops and Products 25, 70–74. https://doi.org/10.1016/j.indcrop.2006.07.004

Vertucci, C.W., Leopold, A.C., 1984. Bound water in soybean seed and its relation to respiration and imbibitional damage. PLANT PHYSIOLOGY 75, 114–117. https://doi.org/10.1104/pp.75.1.114

Powell, A.A., Oliveira, M.D.A., Matthews, S., 1986. The role of imbibition damage in determining the vigour of white and coloured seed lots of dwarf french beans (phaseolus vulgaris). Journal of Experimental Botany 37, 716–722. https://doi.org/10.1093/jxb/37.5.716

Duke, S.H., Kakefuda, G., 1981. Role of the testa in preventing cellular rupture during imbibition of legume seeds. PLANT PHYSIOLOGY 67, 449–456. https://doi.org/10.1104/pp.67.3.449

PowellL, A.A., Matthews, S., 1981. A physical explanation for solute leakage from dry pea embryos during imbibition. Journal of Experimental Botany 32, 1045–1050. https://doi.org/10.1093/jxb/32.5.1045

Hampton, J.G., Tekrony, D.M., 1995. Handbook of vigour test methods. The International Seed Testing Association, Zurich (Switzerland).

Moncaleano-Escandon, J., Silva, B.C., Silva, S.R., Granja, J.A., Alves, M.C.J., Pompelli, M.F., 2013. Germination responses of jatropha curcas l. seeds to storage and aging. Industrial Crops and Products 44, 684–690. https://doi.org/10.1016/j.indcrop.2012.08.035

Thornton, J.M., Powell, A.A., Mattews, S., 1990. Investigation of the relationship between seed leachate conductivity and the germination of brassica seed. Annals of Applied Biology 117, 129–135. https://doi.org/10.1111/j.1744-7348.1990.tb04201.x

Abdullah, W.D., Powell, A.A., Matthews, S., 1991. Association of differences in seed vigour in long bean ( vigna sesquipedalis) with testa colour and imbibition damage. The Journal of Agricultural Science 116, 259. https://doi.org/10.1017/s0021859600077662

Powell, A.A., 1986. Cell membranes and seed leachate conductivity in relation to the quality of seed for sowing. Journal of Seed Technology 81–100.

Yaklich, R.W., Kulik, M.M., 1979. Evaluation of vigor tests in soybean seeds: Relationship of the standard germination test, seedling vigor classification, seedling length, and tetrazolium staining to field performance1. Crop Science 19, 247. https://doi.org/10.2135/cropsci1979.0011183x001900020019x

Matthews, S., Powell, A., 2006. Electrical conductivity vigour test: Physiological basis and use. Seed Testing International 131, 32–35.