Global markets were not lacking in precarious unknowns. Italy just added another.

As voters on Sunday emphatically rejected constitutional changes aimed at streamlining government and making it easier to revive a moribund economy, they enhanced concerns that Italy’s banks could spiral into a disaster. They reinvigorated worries about the endurance of the euro currency and broader European economic integration. And they amplified the sense that Europe is a land of disappointing growth, political dysfunction and seething populism.

“Existential crisis” had not been on the ballot, but that was essentially the result. The lopsided tally against the reforms — nearly 60 percent rejected them — prompted the resignation of Italy’s prime minister, Matteo Renzi, leaving Europe’s fourth-largest economy without clear leadership.

As world markets absorbed the result, investors soured on Italian banking stocks. Shares in Monte dei Paschi di Siena, which was involved in Italy’s grandest banking fiasco, surrendered 4 percent on Monday on expectations that a private sector rescue devised by Mr. Renzi had been killed.

Investors initially pushed down the euro before it recovered. They cut the price of Italian government bonds, lifting the yield — a sign that investors will demand greater reward for the heightened risks of lending to Italy. Investors also unloaded Spanish and Portuguese government bonds.