# Reverse Sap Flow from Fruit

## TL;DR

This study explores how watermelon plants reverse sap flow from fruit to other parts, revealing how this process helps plants survive drought.

## Contribution

The study introduces a new method combining wearable sensors and environmental monitoring to investigate reverse sap flow mechanisms.

## Key findings

- Reverse sap flow is caused by a water supply-consumption imbalance in plants.
- Rapid light surges and soil drought trigger reverse sap flow in watermelon plants.
- Reverse sap flow improves plant drought resistance by redistributing water.

## Abstract

Sap flow serves as the primary carrier for water, nutrients, and signaling molecules, playing a crucial role in fruit development by delivering these essential constituents to the fruit. While the efflux of sap from fruit to other organs (termed reverse sap flow) has been observed in plants, its underlying mechanisms remain unclear due to a lack of effective methodologies for comprehensive studies. Here, we pioneered the integration of real-time sap flow measurements from novel plant-wearable sensors with synchronized environmental monitoring, establishing a multimodal data framework to systematically decode the endogenous causes and exogenous triggers of reverse sap flow in watermelon plants. Our experimental results reveal that plant water supply–consumption imbalance is the core endogenous cause of reverse sap flow, which is induced by two external triggers in the natural environment: rapid light intensity surges and soil drought. Furthermore, a long-term drought stress experiment illustrates that reverse sap flow from the fruit enhances the drought resistance of plants by adjusting water redistribution within the whole plant. This study challenges the unitary view of fruit solely as a “sink” in the traditional source–sink theory, further refines the understanding of the source–sink paradigm, and provides a novel mechanism and insight for plant drought tolerance strategies.