# Exploring the influence of nanosilica on monoterpene biosynthesis, PAL1 and LS gene expression in cumin (Cuminum cyminum L.) under water-deficit stress

## TL;DR

This study shows that nanosilica can boost essential oil production in cumin under moderate drought by enhancing key gene activity, but its benefits decrease under severe drought.

## Contribution

The study introduces nanosilica as a novel tool to enhance drought tolerance and essential oil yield in cumin through gene regulation.

## Key findings

- Nanosilica significantly upregulated PAL1 and LS gene expression, increasing essential oil yield in cumin under moderate drought.
- Essential oil yield in cumin increased from 2.19 to 5.14 kg/ha in the Isfahan landrace with 6 mM nanosilica at 60% field capacity.
- Nanosilica's effectiveness declined under extreme drought, with cuminaldehyde content dropping over 50% despite treatment.

## Abstract

Drought stress considerably influences plant growth, physiological processes, and secondary metabolite synthesis, such as essential oil in Cumin (Cuminum cyminum L.), a medicinal and aromatic plant. The present expriment explores the possibility of using nanosilica (nSi) to enhance essential oil yield in cumin under various drought conditions. The cumin seeds utilized in this study were sourced from pakan bazr Isfahan, an Iranian seed company. Two Iranian cumin landraces, Isfahan and Semnan, were subjected to three drought levels (60, 40, and 20% of field capacity, FC) combined with three concentrations of nanosilica (0 as control, 4, and 6 mM) using a factorial experiment based on a randomized complete block design (RCBD). The study evaluate the levels of phenylalanine ammonia-lyase 1 (PAL1) and limonene synthase (LS) expression, essential oil yield and quality through the utilization of gas chromatography-mass spectrometry (GC-MS).

The results indicated that nSi application considerably upregulated PAL1 (peaked at 60% FC, increasing by 3.3 fold-change with 6mM nSi application) and LS expression (up to 3.6 fold-change under moderate drought) under drought conditions, promoting drought tolerance and essential oil production. The highest essential oil yield was recorded at 60% FC with 6 mM nSi, which was raised from 2.19 to 5.14 Kg.ha-1 in Isfahan landrace and from 2.92 to 7.22 Kg.ha-1 in Semnan landrace. The α-pinene (reaching 8.6 at 20% FC, 4 mM nSi, Isfahan landrace), β-pinene (31.5 at 20% FC, 4 mM nSi, Semnan landrace), and cuminaldehyde (6.3 at 60% FC, 4 mM nSi in Semnan landrace) content of monoterpenes changed with the variation of drought stress and nSi treatment, indicating continuous improvement of secondary metabolite synthesis by nSi under stress.

Findings demonstrate that nanosilica enhancing PAL1 and LS, key metabolic pathways genes in cumin under drought stress. Nanosilica’s efficacy diminished under extreme stress, where cuminaldehyde content still dropped by over 50% despite treatment. These results underscore nanosilica’s potential to improve secondary metabolite and crop resilience under moderate water deficit, though integrated strategies are required for severe drought conditions.