TMTM sustained root growth under sulfur limitation
Imbalances in the sulfur pool have severe consequences for plant growth and yield (Zhaoet al. , 1999; Lunde et al. , 2008; Jobe et al. , 2019). Under LS, biomass production and root growth were significantly reduced (Figure 3 and 4). This could be restored by the application of TMTM in low doses. We propose that TMTM maintains the sulfur homeostasis and allows root growth which is comparable to that under HS conditions (Figure 4). Furthermore, it appears that excess TMTM tilts the sulfur homeostasis and shifts the sulfur towards the secondary metabolite pool, resulting in reduced plant biomass production and root growth (Figure 3 and 4).
Growth regulation by TMTM via sulfur homeostasis is further supported by the response of WT and slim1 seedlings to high TMTM dose. 1000 µg TMTM inhibited root growth in WT seedlings, but not inslim1 (Figure 4). Apparently, lower doses of TMTM stimulated root growth in LS because the volatile influences the sulfur homeostasis. As a result, the root growth was comparable to seedling´s growth on HS without the volatile. However, the high dose (1000 µg) of TMTM could provide too much sulfur to the LS-grown WT seedlings, which may result in the activation of stress responses and ultimately growth retardation. On the other hand, because slim1 could not mobilize sulfur from its secondary metabolites (Maruyama-Nakashitaet al. , 2006), these seedlings showed a higher tolerance to excess TMTM. The different response of the two genotypes to excess TMTM is consistent with the idea that TMTM-induced changes in the sulfur homeostasis influence root growth.