# Comprehensive Assessment of the Dynamics of Banana Chilling Injury by Advanced Optical Techniques
## 4 Discussion
Increased contribution of the quantum yield of non-light-induced quenching [64], \(Y_{\rm NO}\), an indicator of the sum of non-regulated heat dissipation and fluorescence emission mainly due to closed PS II reaction centers [40], could have been expected (but was not evident), if a sustained contribution of non-photochemical quenching [63] was active. Consequently, it can be assumed that there is no measurable chilling effect on the total efficacy of the non-photochemical protection mechanisms and, thus, on the ability of the fruit to potentially use the non-photochemical dissipation of absorbed light energy. This is further substantiated by the full and rapid relaxation of light-induced increases in both regulated and non-regulated non-photochemical quenching upon return to dark conditions in all samples irrespective of storage temperature. This, in addition, convincingly highlights that chilling does not impair the overall photosynthetic competence of the banana fruit. It has been stressed that for the correct and detailed mechanistic interpretation of any variation of \(F_{\rm v}/F_{\rm m}\) and other CFA parameters, the potential changes in the optical properties of the produce need to be assessed [64], as carefully done in the presented study. In this context, the fact that the remission spectra of bananas were not affected during cold storage, irrespective of the prevailing temperature, ruled out any influence on the measurement and the evaluation of the above fluorescence parameters. Thus, the decline in \(F_{\rm m}\) may highlight the reduction of the functional efficiency of PSII RC [59]. The pronounced and very specific changes of the performance index, \(PI_{\rm ABS}\)[45; 48], of fruit stored at the respective low temperatures further substantiated this notion. [PERSON] et al. [59] regarded the performance index \"as the most reliable criterion for the evaluation of dark chilling stress\", assuming that this parameter \"expresses the accumulation of all responses of the photosynthetic apparatus\". The above authors also assumed that during dark storage, chilling temperatures negatively affect the intrinsic function of the photosynthetic electron transport chain. This effect might be mediated by the reduction of the fluidity of the thylakoid membrane, which, in turn, affects the mobility of plastoquinones and plastocyanines below the known temperature threshold. As a result, the overall potential photosynthetic performance is impaired without a destruction of the photosynthetic apparatus. The former is indicated by the concomitant decline in \(PI_{\rm ABS}\) and \(F_{\rm m}\), while the constancy of \(F_{\rm v}/F_{\rm m}\) highlighted the latter. Besides the above-mentioned mechanisms, \(F_{\rm m}\) may, of course, also decline simply due the reduction of the chlorophyll content, i.e., the overall the ability to fluoresce [35; 64]. This could be expected if the chilling-induced oxidative stress resulted in a gradual destruction of the PSII core protein complexes concomitantly leading to the release and the final degradation of chlorophylls as assumed by [PERSON] et al. [36] for cucumbers stored at low temperatures in darkness. Any decrease in the contents of chlorophylls, however, is ruled out by the constancy of NDVI in all samples irrespective of the prevailing storage temperature. It was shown manifold that NDVI indeed closely reflected changes in the chlorophyll contents of fruit and leaves [49; 51; 52; 60], and, thus, clearly substitutes chemical analysis of these pigments. Anyway, the presented results rule out any possible effect of a decreased chlorophyll content on \(F_{\rm m}\) but may further support the view that chilling does not impair the structural intactness of the photosystems. The constancy of the chlorophyll content as observed in the present study also nicely fits to findings of earlier investigations on the chilling effects in banana [14] but contradicts recent reports indicating that chilling conditions tended to accelerate chlorophyll degradation in green-ripe fruit [16; 26].