Physiological studies of plants reveal that diffusion of ethylene, into and out of plant tissue, is responsible for regulating and stimulating various growth and developmental activities such as ripening of fruits (Yang, 1995; Alexander and Grierson, 2002; Atta-Aly and Brecht, 2000; Klee, 2002; Fan et al., 1999; Fan and Mattheis, 2000), opening of flowers, and senescence (Abeles et al., 1992). Ethylene also induces loss of cellular turgor, chlorophyll and pigment degradation, irregular opening, yellowing or shedding of flowers and leaves, premature death and hence loss of product quality (Serek et al., 2006). 1-Methylcyclopropene (1-MCP), a cyclic olefin, is used commercially as a synthetic plant growth regulator and is applied onto post-harvest agricultural products such as fruits (including climacteric and non-climacteric), flowers and vegetables to retard their ripening and thus prolong their shelf-lives (Sisler et al., 2003; Blankenship and Dole, 2003). Because of structural similarities, 1-MCP works as a nontoxic antagonist of the natural plant hormone – ethylene, interacts with and then covalently binds to ethylene receptors, thus blocking its absorption completely and inhibiting its hormonal action (Sisler and Serek, 1997; Blankenship & Dole, 2003; Watkins, 2006; Sisler et al., 2006). The affinity of 1-MCP to the ethylene receptors is ten times greater than that of ethylene (Watkins, 2006), which means a low concentration of 1-MCP is sufficient for application to horticultural products (Figure 1). 1-MCP blocks the activities of ethylene (Serek et al., 1995; Sisler and Serek, 2003; Blankenship and Dole, 2003) for a certain time until all 1-MCP diffuses from the binding sites or new ethylene receptors develop (Bayer 1976a, 1976b, 1978; Veen, 1983).
It was also reported that (Kawakami, E.M., Oosterhuis, D.M., Snider, J.L., 2010) the use of 1-MCP in an open field (It was not, this work was done in a growth chamber!) has a potential impact on crop yield by affording protection (NOTE:delete them) from an environmental stressor such as drought in which 45% (Bot et al., 2000) of the total world’s agricultural lands are subjected to continuous or frequent drought conditions which hamper the overall crop yields substantially. (Can’t use this, it’s copied directly from Kawakami et al.) Say the following instead: It was also reported that (Kawakami etc) the use of 1-MCP, in conditions simulating an open field, has potential impact on crop yield in open fields by affording protection from an environmental stressor such as drought which limits crop yields in 45% of the world’s land dedicated to agriculture (Bot et al., 2000). Under environmental stresses, increasingly produced ethylene by plants play a serious role in shedding of leaves. As a pre-harvest treatment, 1-MCP can also be used to block the ethylene receptors and lower the effect of water stress level in plants which is initiated by absorbing ethylene and thus prevent premature wilting, chlorophyll degradation and leaf yellowing and eventual death of crop plants (Chow & McCourt, 2006; De Paepe & Van der Straeten, 2005).
1-MCP is an odorless gas at ambient conditions (b.p. 9-12 oC), which is difficult to handle in an open environment At present, there is no technology available for application of 1-MCP in open crop fields conveniently and effectively. However, the reported B-MCP analog complexes (Sarker et al., 2015; Sarker et al., 2016) (Figure 2) have shown significant potential to be directly used in open fields by releasing 1-MCP over a long time period depending on individual structure. The effectiveness of these complexes to inhibit tomato ripening was demonstrated in an open, laboratory environment and reported in our earlier publication (Sarker et al., 2016).
The chemistry involved in releasing 1-MCP from a B-MCP analog is controlled by a hydrolysis reaction (Sarker et al., 2015) and the rate of this hydrolysis reaction mainly depends on the different moieties attached to the central boron atom. Therefore, 1-MCP is found to be released at different rates from different complexes which are useful depending on the application. For practical application in an open field, it is important to analyze the effectiveness of these B-MCP complexes under different environmental conditions of temperature and humidity and the 1-MCP release properties of the complexes when in contact with water such as wetted area, pH and water content. In this paper, we have reported the synthesis and potency of two new B-MCP complexes (BNMB, BPNMB; Figure 3) which are found to be similar in releasing 1-MCP due to the electronic effect staged in attached moieties and also from the hydrophobic and hydrophilic characteristic of the molecules as a whole. A comparative release pattern of 1-MCP from BPMB, BNMB and BPNMB has been studied to understand the overall mechanism.